The leather trade can cause terrible deforestation in the Amazon, but this new Gucci Jackie bag is made of hide that has been ethically produced

Something important happened at Paris fashion week on Monday. No, not Hedi Slimane's grunge revival or how laundromat checks are becoming a thing or Bono turning up in Stella McCartney's front row. Something, you know, important-important.

Livia Firth, the Observer's Lucy Siegle and Italian Vogue's Franca Sozzani hosted a panel discussion in the Brazilian embassy to mark the extension of Firth's ethical red carpet landgrab, the Green Carpet Challenge, into handbags.

This special edition of Gucci's iconic Jackie bag is pioneering a project to curb the deforestation of Brazilian landforest caused by cattle ranchers. If you missed Lucy's story in the Observer mag at the weekend, read it here. Deforestation and leather production is not exactly a sexy issue, so kudos to Siegle and Firth for persuading Gucci to take it on. As Firth put it, the bag takes "an unfashionable agricultural story, and gives it a beautiful twist".

Karl Lagerfeld channels Chanel history for autumn/winter showcase, with accessories referencing his own inimitable style

Karl Lagerfeld is probably the most recognisable fashion designer in the world, but the name in lights at Paris fashion week is that of Chanel, not Lagerfeld himself. Lagerfeld has presided over Chanel for 30 years, but remains the Thomas Cromwell of this kingdom. He is puppetmaster and strategist, too wily to allow his own ego to derail a masterplan.

The Chanel catwalk shows, held each season inside the cavernous Grand Palais with a cast of hundreds and an audience of thousands, bring central Paris to a standstill in a blare of traffic whistles.

The first message is one of scale. Recent show sets have featured wind turbines, icebergs and a 12-metre-long golden lion. On Tuesday, the space was dominated by an enormous rotating globe in the centre of the catwalk, a sparkling flag bearing the double-C trademark pinned to show the location of each Chanel boutique. It was an impressive show of global power – who knew Chanel had not one, but two boutiques in Honolulu? – but also neatly broadened the focus of the event, from the arcane procedures of a Paris show – the ritualistic pomp, the place names in traditional calligraphy – to the reality of a luxury brand in the 21st century.

But what matters most at any fashion show is beauty. And since there can be few human beings whose heart does not soar at the familiar yet awesome image of a gently spinning Earth as viewed from space, the globe was a triumphant centrepiece.

For all the space age symbolism, this was the most traditional Chanel collection Lagerfeld has shown for a while. (Perhaps that's what perspective does to you.) Ignore the crazy accessories and the look centred on the key moments in the Chanel story. Bouclé tweed suits came in glittering chic monochrome, in a melange of crimson and black, or in soft heathery pinks. Day dresses came in the drop waist silhouette so chic in Coco's heyday. For evening, elegant silk dresses in softly voluminous shapes took their cue from the atelier rather than the street.

But to ignore the crazy accessories would be to miss not only the fun, but a fundamental element of this brand. Cricket-ball sized globes dangled from Chanel's famous gold chains as next season's talking-point handbag. Furry, close-cropped aviator hats in bright colours brought a dash of the daredevil, globetrotting spirit of Amelia Earhart – a woman of the same era as Coco Chanel, of course – and conjoined it with the vogue for neon beanie hats which has seized the growing fashion blogger population during what has been an unusually chilly month of fashion shows in New York, London, Milan and Paris. The Earhart reference echoed through the jackets, which were cut longer than usual and with a multitude of pockets, flying-jacket style. Lagerfeld himself made cameo appearances woven into the catwalk persona, as he always does. This season he was represented by the leather leggings and by a staggering variety of fingerless gloves. One pair had the tiniest of windows cut into the leather over the fingernail, the better to showcase the latest brand of Chanel nail polish – a rich red called Accessoire, a bottle of which was handed to each show attendee in a beribboned Chanel bag. The devil is in the detail, and Lagerfeld is not one to miss a trick.

Collection based on ecclesiastical wear, with ornate ruffs and cartridge-pleated skirts redolent of pomp and ceremony

In fashion as in comedy, timing is everything. Sarah Burton, designer of Alexander McQueen, found herself with a scheduling issue when the due date of her twin daughters clashed with McQueen's slot at Paris fashion week, a situation the brand resolved by downsizing this season's show to a small presentation of 10 outfits. But in another sense, her timing could not have been more apt. Her collection was based on ecclesiastical wear, a hyperstyled, ultra-chic take on the wardrobes of popes and nuns, on cardinals' robes and communion gowns. (Burton has already pulled off a fashion coup when she dressed the Duchess of Cambridge for her wedding; is a commission for the next papal inauguration so very far fetched?)

This being McQueen, the grand gowns had more than a hint of the gilded cage about them. The models' heads were enclosed in diamond-patterned gilded cages, studded with teardrop pearls; their bodies within embroidered bodices, and hoop skirts. The fishnet tights studded with pearls might be a little risque for the Holy City, but the ornate ruffs and lavishly cartridge-pleated skirts were redolent of pomp and ceremony.

Impulse toward loucheness and mystery is an about-turn from last season's Paris Fashion Week show

It is late at night, in a grand hotel in Paris. A door opens and Kate Moss emerges, wearing only a semi-transparent dress over knickers. She sashays the length of the corridor, opens the door to a different room, and closes it behind her.

Marc Jacobs, it is fair to say, knows how to get the attention of a jaded world. This was the vignette played out at his Louis Vuitton show at Paris Fashion Week on Wednesday morning.

Instead of a traditional catwalk, Jacobs had a theatrical set of a hotel corridor built, complete with chic pale blue wallpaper, thick carpet and 48 wooden doors. The lights dimmed and doors began to open, each revealing a woman dressed with glamour but a hint, or more, of impropriety.

Sometimes there was merely the suggestive flash of a lace slip visible under an elegant wool coat, or a deep split in a pencil skirt; at other times a dress was no more than a negligee, held up by the flimsiest of straps, or a coat covered nothing more than a pair of – what else – French knickers.

Hotels are rich territory for Jacobs because the Louis Vuitton brand is built on luxury travel, and grand hotels are where luxury travel meets sex appeal. (As each door opened, a vintage Vuitton trunk could be glimpsed in the room set as the model emerged.) So it was appropriate that Jacobs dressed for the occasion so as to suggest he felt very much at home, taking his bow in a pair of silk pyjamas. (Not any old pyjamas, naturally; a collaboration between British artists Jake and Dinos Chapman and Kim Jones, Louis Vuitton's menswear designer, they will be in stores next season.)

Backstage after the show Jacobs said the show was about "a woman who gets dressed up, but then decides she'd rather stay in her hotel room. There's a certain decadence to that. I had in mind certain friends of mine, who walked in the show but shall remain nameless, with whom I've spent many, many nights getting dressed up in hotel rooms."

A gentlemen never tells, but the name of Moss, a close friend of Jacobs, hung heavy in the air.

Jacobs likes to make the fashion world race to keep up with him. The impulse toward loucheness and mystery was an about-turn from last season's show, which was based on checkerboard grids and orchestrated with military precision, the models delivered to the catwalk in pairs, on synchronised escalators.

"Everything's a reaction," agreed Jacobs. "Last season was so conceptual, very much about rigidity and not about feeling. So of course this is a contrast, a show about romance and emotion and eroticism."

He named Gloria Swanson and Juliette Greco as muses of the season. "It's Left Bank, but also Hollywood," he said. If the exquisite lace slips and quietly expensive handbags were quintessentially Parisienne, the ankle strap sandals, mink trims and maribou feathers added a sense of starlet glamour.

The sense of deliberate anonymity was echoed in the season's handbags. Classic handbag styles of the label, such as the Speedy holdall and the sleek Pochette, were tucked under almost every arm, but the Monogram and Damier motifs that have been prominent in recent seasons were nowhere to be seen.

The new wave of ruffles owes more to fine art than seaside doilies. Jess Cartner-Morley wears a dress by Lanvin, and points to ruffles on the high street

You've seen the trends, now here's the gossip – from Alex Ferguson's unexpected influence on style to some shocking news about shoulder bags

1. The biggest influence on fashion in 2013: Alex Ferguson

You know how Alex Ferguson always says no player is bigger than Man United? That attitude is one that fashion-industry bosses are now adopting. The new generation of designers working as hands-for-hire for the major fashion houses will not be allowed to become gods in their own right in the way that the previous generation – Tom Ford at Gucci, John Galliano at Dior – were able to do. François-Henri Pinault, the head of PPR, has made it clear that, post-Ford, the brand will always be the front-of-house product, not the designer's creativity. (As for LVMH – well, we all know how the allowing-Galliano's-genius-to-blossom-unchecked strategy panned out.) The result is that the new generation of designers – Wang at Balenciaga is the obvious example – are duty-bound to promote the codes of the house, or the DNA of the brand, at every turn. Which is fine, and interesting to a point. But when it gets to be in every single sleeve-shape, it is in danger of becoming a little bit boring.

2. The counter-trend to the Alex Ferguson School of Fashion: It's Just What I Want To Wear, As A Woman

So basically, half the designers in Paris have bosses who are running around bashing them over the head with fashion history books, and the other half are like "I'm so glad I don't have that, I'm so free", and as a result they are enjoying showing off about how their collections are all about a personal emotion. Paris fashion right now can be divided into Team Codes of the House and Team It's Just What I Want to Wear, as a Woman.

3. The shoulder-bag is dead

You know your bag? That great big bulging one, that you sling over your shoulder? Nobody at Paris fashion week has a bag like that. The type of handbag owned by 99.9999% of British women – sack-like, practical shoulder strap for comfort even when it weighs a tonne, capacious enough for spare shoes/the stuff you need to get from Tesco on the way home – does not exist at Paris fashion week, either on the catwalk or among the audience. Evening bags are clutchbags or pouches; day bags are slightly bigger pouches that should be hugged to the body. Shoulder straps must be removed or tucked out of sight. If you absolutely must have a bag bigger than a clutch/huggable pouch (ie if you are British) it should have short straps, like a basket, so that you hold it in your hand rather than sling it over your shoulder.

4. The Black Crows v The Peacocks

Suzy Menkes, quiffed queen of the front row, got everyone's La Perlas in a twist with an article attacking that new breed of fashion-industry professional, the blogger. (In Menkes's piece, he black crows are the old-school fashion editors, who wore something wonky and dour and Japanese; the bloggers, with their statement heels and bare legs and look-at-meeee outfits, are the peacocks.) Hard to know where to stand on this. My personal respect for Menkes is immense, but on the other hand I am also seriously impressed by bloggers who are able to shoulder-robe a jacket while taking a photo. Can't we all just be friends?

5. It is all about a fringed bob

Cara who? This Paris fashion week has been all about Karlie Kloss and her gorgeous bob-with-bangs, as the Americans call it. Michelle Obama's already on this trend, and once The Great Gatsby comes out in May it'll go nuclear, mark my words.

6. In Paris, leopardprint never goes out of style

Like, ever, as Taylor Swift would say.

7. This winter's coat isn't going to cut it next winter

If you invested in a tailored-classic-coat this season thinking it would be a timeless piece, prepare to be annoyed, because next season is all about a fairytale coat. Choose from cutesy and childish (the duffel, as seen at Saint Laurent); Grimm brothers hooded cape (Valentino); or Wicked Stepmother Fur (just about everywhere). And yes, I know you think you don't care about trends but ... get your coat properly cleaned before you put it away this spring, just in case you don't see it again as soon as you think, OK? Please. For me?

'Early adoption of the modern frill is a high-risk strategy. The pioneering frill-seeker appears to have got dressed up in something fussy and fancy, not something chic and stylish'

For a long time, frills have been a detail added to make things look fancy. Fancy is not, you may have noticed, a term of high praise in this column, or any fashion column in the last half-century. Fancy isn't chic, or stylish. Fancy is quite the opposite. The aesthetic of our age demonises clutter, and frills have become little more than visual clutter. Frankly, we have become snobbish about frills.

The narrative of fashion being what it is, it was therefore only a matter of time until the frill made a resounding comeback. Catwalk shows for Lanvin and Givenchy in Paris, and for Gucci in Milan, all included dresses with unmissable frills.

Unmissable is the key word here. The frill as rebooted for summer 2013 is a strident, definite sort of a frill. The changes are marked in simplicity, texture and scale: rather than narrow, soft frills repeated ad infinitum around the edge of a garment like cocktail-hour small talk, you have one bold, stiffened, cap-locked detail. Where traditional frills echoed the neat symmetry of a suburban flower bed, the modern frill is asymmetric and unexpected. The frill on the dress I am wearing today reminds me less of petals or sand ripples than of the Japanese print the Great Wave Off Kanagawa. It is elegant, yet a force to be reckoned with.

Early adoption of the modern frill is a high-risk strategy. To those as yet unenlightened, the pioneering frill-seeker appears to have got dressed up in something fussy and fancy, rather than chic and stylish. You could put together a moodboard – postcards of the Great Wave, catwalk photos, perhaps a Brancusi– to enlighten people, but I wouldn't. A bit too Jehovah's Witness.

Instead, enjoy confusing people. Experiment with a frill – this is Lanvin, but try Zara– and wear it somewhere frill-free. There's no point fudging things by wearing frills to a garden party; wear your frill, with pride, to places with poured concrete floors and Borgen-inspired lighting.

Your "frill", not "frills", you will have noticed. The modern frill is singular – one great surging wave, not a choppy sea. The frill may be back, but you can have too much of a good thing.

• Jess wears dress, £1,950, by Lanvin, from Harrods. Block heel sandals, £60, topshop.com.

Photograph: David Newby for the Guardian. Styling: Lucy Trott at Carol Hayes Management. Makeup: Dani Richardson using Sisley Cosmetics.

Jess Cartner-Morley picks out a few retro sportswear items to suit your budget

'Now that the tracksuit doesn't belong in your gym-gear drawer, it has been upgraded to your wardrobe'

Fashion journalists, while keen to keep you bang up to date as to where Alexa Chung stands on Breton stripes and Miranda Kerr's current thinking vis‑a‑vis Aviator shades, sometimes let substantial shifts in the nitty-gritty of Clothes People Wear go entirely unreported. Often, I suspect, this is because there are no red carpet shots of Chung or absurdly glamorous LAX departure lounge snaps of Kerr with which to illustrate said nitty-gritty. Happily, we have no need of such eye candy here because, in the words of one of my foremuppets, Miss Piggy, this column is all about moi.

Now this is fortunate, because there has been a development in Clothes People Wear which has slipped under the glossy radar. Specifically, in the clothes women wear for exercise: the gym, Pilates, whatever. The default outfit for this used to be the tracksuit. Tracksuit bottoms, sports bra/vest, then a loose top or hoody. Tight running trousers existed, but they marked you out as Serious About Fitness and/or Proud Of Thighs.

But this has changed. On the yoga mats, treadmills and running tracks of the nation, the Lycra-infused running trouser has taken over. Rather than the tight trouser marking you out as extra-serious, the tables have turned – wear tracksuit bottoms and you are labelled as the lazy cow using your gym membership for the third time this year.

But I'm not here to ridicule your outdated exercise gear or make you feel guilty for missing Zumba. My point is that the tracksuit has graduated from being sportswear into being retro sportswear – a quite different category, and one which fashion has always happily plundered for inspiration. (See: baseball jackets.) Now that it doesn't belong in your gym-gear drawer, it has been upgraded to your wardrobe. Which is why the smartest London and Paris boutiques have waiting lists for sweatshirts this season, and why smart tracksuit bottoms are proving themselves to be more than a one-season wonder. The sporty lettered graphic, the tracksuit bottom, the hi-top trainer: today, I am in head-to-toe retro sportswear. In other words, I'm in fashion.

• Jess wears blue 'H' cotton sweater, £240, houseofholland.co.uk. Track-style trousers, £39.99, Zara zara.com. Suede wedge sneakers, £149, by Ash, from my-wardrobe.com.Photograph: David Newby for the Guardian. Styling: Lucy Trott at Carol Hayes Management. Makeup: Dani Richardson using Sisley Cosmetics.

The Starman leotards and Ziggy Stardust bodysuit are still dazzling, but tailoring is the real star of this show

Read music critic Alexis Petridis's verdict on the exhibition

How much of this exhibition is fashion? David Bowie would probably say that none of it is. Bowie has always said he isn't interested in fashion, only in wanting his music "to look how it sounds".

And yet right from the off – a metallic, striped Ziggy Stardust bodysuit designed by Kansai Yamamoto, who in 1971 was the first Japanese designer to show in London – this show is full of clothes that have shaped fashion history, from the Starman leotards, still arresting after all these years, to the turquoise Life on Mars suit and tie, so theatrically slender that it had to be let out by two inches when Kate Moss wore it; from the Aladdin Sane lightning-flash makeup that has inspired a thousand magazine shoots to the sharp-shouldered suits of the Diamond Dogs tour, which were a formative influence on Hedi Slimane, current designer of Yves Saint Laurent.

Displayed alongside that first Ziggy bodysuit is an early video of the artist duo Gilbert & George explaining that, as they see it, "living is one big sculpture". This is a first principle of Bowie as envisaged here: one of the very first photographs shows him aged 16, with his band the Konrads. His suit and quiff are standard issue for their time, but what makes the image is an instinct for line, silhouette and pose, an innate understanding of how to shape his body for effect.

Image cannot be neatly cordoned off to one side of Bowie. It is part of a three-dimensional experience that David Jones orchestrated for all his characters – not just the Thin White Duke or the Starman, but for David Bowie himself. This show – absorbing, unsettling, full of extraordinary details – captures that sense of immersive experience that makes Bowie electric.

The Bowie fanatics will come here to pay homage to the self-expression of a genius, but what is fascinating for a wider audience is the way Bowie interacts with and shapes popular culture. Whether it's wearing kitten heels with a Thierry Mugler suit or adopting Japanese silhouettes before that aesthetic was widely known in the west, he articulates and synthesises the avant garde for a mass audience. His ability to be simultaneously androgynous and highly sexual, game-changing in the 1970s, still resonates through popular culture today. Previously unseen footage of the Diamond Dogs tour, (which never came to the UK) shows the extent to which that tour, which required 35 people to build the set each day, invented the idea of the theatrical tour that is now the multimillion-pound stadium pop industry.

The exhibition is sponsored by Gucci, whose designer Frida Giannini is a longtime fan of Bowie, and who recently told Vogue: "Bowie's shameless androgyny helped women express their masculine strength without losing their feminine glamour and sensuality." (The sweet irony of a show that celebrates self-expression and the potency of Bowie's raw, snaggle-toothed type of glamour being sponsored by a global megabrand is a contradiction that seems quite apt.)

Catsuits tend to grab headlines. But from a fashion angle, the true stars of this show are the suits. Bowie's tailoring is a joy to be savoured. When Slimane moved into his minimalist design studio on taking over Dior menswear, he added just one photo to the white walls, of Bowie in 1975 presenting a Grammy award to Aretha Franklin, wearing a wide-lapelled black suit, white bow tie and black fedora hat. That suit is here. The mustard suit in which Bowie was photographed by Terry O'Neill in 1975 is also here, as is the photograph: the cut is so startling, the tightly waisted jacket and sensual femininity of the balloon-hipped trousers so jarring with the extraordinary Colmans shade and the razor-sharp lapels, that it is easy to see why designer Phoebe Philo cited the suit as an inspiration for a Céline womenswear collection in 2011.

Ziggy Stardust might get top billing but David Bowie, modern dandy, is the most stylish of all the characters on this stage.

The check has gone haute. Jess Cartner-Morley picks out a selection for your wardrobe

'This season, the check has gone haute'

Checks are practical. Checks are flannel shirts and cheerful tablecloths, nursery soft furnishings and aprons. Checked sleeves are sleeves that are made to be rolled up. Except not this season, because the check has gone haute.

The chessboard check, a stark grid of square tiles in traditional black and white, or in yellow and white, is the king of the fashion game. The Louis Vuitton dresses that started the ball rolling at Paris fashion week last October staked a claim to the red carpet early on, and have been holding high-profile positions on various glossy magazine covers since the new year. They are in high demand, despite carrying a price tag equivalent to a mid-priced family car and being wildly unflattering on anyone bigger than a British size 6.

What you see today used to be called a windowpane check, but in honour of the checkerboard craze, I'm rechristening it the noughts and crosses check. Noughts and crosses is a game everyone can play, while chess is for the elite, you see? Similarly, the noughts and crosses check is a check anyone can wear, while the chessboard check is for people who are richer and thinner – in other words, the fashion world's version of the elite.

The noughts and crosses check has a catwalk pedigree all of its own – this dress is by Sportmax – and, being more wearable, has been more widely picked up on the high street. To amplify the look, I have chosen the extra-hot-sauce version, all asymmetry and overlaps; in its more sober version, the noughts and crosses check is not kooky. It has a pleasantly soothing appearance, like a crisp sheet of graph paper.

The trick to styling a noughts and crosses check is not to treat it too reverentially. Style it as you would a stripe: just as a striped collar peeking over the top of a crew neck sweater is a classic, and a striped T-shirt looks good glimpsed under a cardigan or gilet, so the noughts and crosses check will look more chic in small doses. Ease your way in. But be careful: if you let it, this look could become a gateway drug to Louis Vuitton ready-to-wear. And that, my friends, is a dangerous and expensive game.

• Jess wears check dress, £705, by Sportmax, 020-7518 8010. Shoes, £49.99, zara.com.

Styling: Melanie Wilkinson. Hair and makeup: Dani Richardson using Nars Cosmetics.

Kirsty Wark used to wear an Armani jacket as 'a suit of armour', but these days the Newsnight presenter is just as happy discussing a triple-dip recession in Prada or Etro

Kirsty Wark can stand up to some serious cross-questioning on the subject of fashion. Faced with a three-metre rail of the season's finest skirts in our studio, she is formidably well-informed, identifying Marni and Dries Van Noten at 10 paces. Next, her news instincts hone in on the surprise in the designer line-up, a Topshop windowpane check. (She recognises it because she tried to buy it in store, but it was sold out in her size.)

Like a true professional, Wark has come prepared, producing a bottle of Frenzy, this season's Chanel nail polish, from her bag before (the sign of a woman who knows her shops, this) reeling off a list of what size she takes in each designer's clothes. And, crucially – because you get nowhere in fashion without taking risks – she is up for a challenge. Faced with an immense silk-taffeta Christian Dior skirt of the genus that sent Jennifer Lawrence tumbling at the Oscars, Wark barely blinks before putting it on, pronouncing it "very Liaisons Dangereuses", stepping into shoes that are both high and too big for her (a perilous combination) and swishing across the studio.

The hand-painted organza Dior skirt is unlikely to grace the Newsnight set any time soon, but it is an amplified version of a formula that Wark has made her own. "A block colour on top, worn with a patterned skirt, works well for Newsnight," she says. "It's getting that balance between clothes that feel modern and lively enough to be appropriate for the programme, but that are not distracting."

Wark, who at 58 has worked on Newsnight for 20 years, is proof that – contrary to what sometimes seems popular belief – feminism and an interest in fashion can coexist. "Why would it be antithetical to feminism to be interested in style, in design, in line and colour and cut? Why would a desire to feel good about yourself, to look modern, be at odds with feminism? Look at Simone de Beauvoir! She looked fabulous."

Naturally, I'm with her on this one. Surely feminism should allow women to be as complicated and contradictory in their personalities as we allow men to be, with their football teams and fishing rods. "Absolutely! Women are more complicated. Much more interesting." But what about the argument that our culture makes too much noise around women's looks as it is, and feminists shouldn't add their voice to this? "That's a quite separate issue from fashion," she says in that familiar strict Scots tone. "The emphasis on how you look is very narrowly defined in our media. That's the problem. Whereas women can look great in all sorts of different ways. And women on their own terms understand that. Women who are interested in fashion dress much more for women than for men, and with a complex idea of what is stylish which most men just don't understand." I could hug her.

Does power dressing come into her wardrobe choices? "It used to. When I was first in front of the camera, a suit was a suit of armour against the world, to give gravitas. But as you get older, that gravitas comes from within. I remember when I interviewed Mrs Thatcher [in 1990], thinking quite carefully about what I wore: I wanted to look clean, and sharp, so I wore an Armani jacket. Now, it's more a case that there are certain interviews for which you want to choose an outfit you feel confident about and then not think about it again."

After our shoot, Wark is heading straight for the 2pm meeting for that night's Newsnight. Tonight, she's wearing a Prada skirt with an Etro shirt, "which I'd looked at before but didn't buy until I found it for £90 in the Liberty clearance room. I'm a bargain-hunter – of course I am. You don't get a clothing allowance at the BBC, after all. I love Topshop. But things change as you get older. When you're young, you can get away with throwaway clothes, but these days the line has to be better, the fabric has to be better. And I've learned that certain labels and pieces work for me." Prada skirts and Agnès B tops are staples that don't date, or let her down.

On the shoot Wark is warm, easy company, good fun. The only glimpse of her steely side comes when I ask how someone whose hobby is baking – she reached the final of Celebrity MasterChef– stays a size eight. Such a crass question, I know, but I was hoping there was a secret. Turns out there isn't: "Baking is relaxing. I make bread, but I don't eat it myself. I make homemade pasta, but I don't eat it any more. When you get older, you have to be a bit more careful. And I exercise quite a bit – I play tennis every Sunday morning with a friend. Even this weekend, when it was snowing." I must look a bit shocked, because she quickly adds, "But it wasn't a blizzard or anything. Just a flutter, really."

Wark has recently finished her first novel, set on the Isle of Arran. "It's a twin narrative, the story of a 96-year-old woman who has just died and of the young woman who comes to live in her house in strange circumstances. And there's a secret." It's a novel about women's lives and the pull of the land – something Wark, who travels back to Glasgow on the sleeper when she's done at the BBC for the week, feels strongly about. "Older women often have the most extraordinary stories, whether to do with family, or the war, or whatever. But we tend not to notice women beyond a certain age. I wanted to write a story that questioned that, just a little bit."

Dégradé, where colours are gradually shaded instead of clearly demarcated, is the modern version of tie-dye. Jess Cartner-Morley picks out some examples of the look

It's easy to look fabulous when you're young and beautiful. But add a few decades and style makes all the difference… Our 50 best-dressed over-50s know how to make a statement at any age. By Jess Cartner-Morley

'Dégradé, where colours are gradually shaded instead of clearly demarcated, is the modern, minimalist version of tie-dye, though few designers would thank me for flagging that up'

Just when you thought stripes were well and truly over, the domino effect of the trend-that-will-not-die lines up yet another victory. Not content with expanding from the breton to the prison to the zebra crossing stripe, not to mention mutating into the chequerboard and noughts-and-crosses graphic, the stripe has found another guise in dégradé.

Naturally, I'm using dégradé in the pretty, French sense of the word. Banish from your mind all thoughts of credit ratings and ickiness, and, as Diana Vreeland would say, think pink: dégradé as in the embroidered ivory lace couture gown that starred in the recent Valentino exhibition at Somerset House, which had a chiffon insert in shades of pink blending from deep raspberry to pale blush.

Dégradé, where colours are gradually shaded instead of clearly demarcated, is the modern, minimalist version of tie-dye, though few designers would thank me for flagging up that association. The fashion industry has a love-hate relationship with any alternative aesthetic. Designers love the idea of going a bit boho (though they can't quite bring themselves to use the word), but when push comes to shove, there is a squeamishness about stepping outside the sanitised, waxed-and-spritzed comfort zone in which fashion exists. Edgy is all very well, but how about we soften those edges a little?

Which is exactly how you get from tie-dye to dégradé. This is edgy, with the edges professionally blended. Tie-dye in the age of Photoshopped flawlessness.

Dégradé should not look as if it was made in your bathroom sink. It needs to look absolutely deliberate, like a stripe, only more unusual, more interesting, more feminine. It works best on a good-quality fabric, so the effect is smooth and creamy, not grainy and blotchy. A Valentino dress might be out of reach, but a bit of dressing up helps: keep accessories sharp and modern, so perhaps a gold hoop earring rather than a beaded dangly one. There is something meltingly summery about dégradé, but that's no excuse for letting it all hang out. Summer, not gap year, is the watchword, folks.

• Jess wears jumper, £290, by Kenzo, from Browns. Trousers, £345, by Stella McCartney, from Matches.Heels, £165, Russell & Bromley.

Photograph: David Newby for the Guardian. Styling: Melanie Wilkinson. Hair and makeup: Dani Richardson using Nars Cosmetics.

The sweatshirt has got posher and the pencil skirt more casual. Jess Cartner-Morley shows you how to combine the two

'Pencil skirts, which used to be posh, have become more casual; sweatshirts, which used to be casual, have gotten more posh'

You can play this week's fashion game for free. This is one of those Scrabble trends, you see. You just have to take the pieces you've already got in your wardrobe and arrange them in a different way. Enormously satisfying, this, because it addresses that vexing issue: how can it be that, despite having a wardrobe full of clothes, we so often feel we have nothing to wear?

There are certain combinations that we all know work (steak and chips; tailored wool trousers and a silk blouse). And then there are new combinations that used to jar but that we have now all decided to love (see sea salt on puddings). A sweatshirt and a pencil skirt is one of these new combinations.

The reason it works now, when it didn't before, is that both elements have subtly altered their place in our wardrobes in recent years. The pencil skirt, which used to be narrowly constrained to the office and the stuffier reaches of the cocktail circuit, has taken on a looser, sexier personality. The sweatshirt, which used to be strictly gym or sofa wear, has become a statement piece since being adopted by a new generation of Paris fashion designers wishing to semaphore their youthfulness and informality of spirit. To put it another way, pencil skirts, which used to be posh, have become more casual; sweatshirts, which used to be casual, have gotten more posh. The two have inched towards each other and can now meet on common ground.

This is not to say you can just put any two pieces together, like some maddening Scrabble chancer bluffing her way on to a triple-word score. A straight, scratchy, office-basics pencil skirt with a baggy hoodie will make no more sense now than ever. What you need is a new-breed pencil skirt – something a bit slinky, maybe with a split, or a zip, or a print – and a sweatshirt with a precise outline (no sagging elastic on the hips) and some kind of a wink to fashion in the colour or design.

To give you confidence in the two pieces working together, a visual link – such as the gold bits on these two pieces – will help. A dictionary, however, probably won't.

• Jess wears sweatshirt, £29.99, hm.com. Leather skirt, £149, by Per Una, from marksandspencer.com. Heels, £165, russellandbromley.co.uk.

Styling: Melanie Wilkinson. Hair and makeup: Dani Richardson.

Sheer is fashionable, but not in a temperature-raising way. Jess Cartner-Morley shows how it works on this season's clothes

'Even when sexy clothes are on trend, fashion usually finds a way to neutralise the impact'

Fashion is rarely sexy. A side-effect of this being one area of popular culture not dominated by heterosexual men is that it is not all about shaggable birds. Sometimes sexy clothes are, as we say in a particularly antiseptic piece of fashion vernacular, "on trend", but even then fashion usually finds a way to neutralise the impact. Short skirts will be "hot" for a season, but only when worn with a hip-length polo neck in a particular shade of electric-blue waffle. If leather leggings are in, we will be instructed to wear them with enormous neon beanies and hi-top trainers. And so on and so forth.

This is surely a good thing. It would be hard to argue that birds, shaggability of, is an issue cruelly starved of oxygen. A few neon beanies and polo necks are a breath of fresh air, of sorts.

On the subject of breathing fresh air, of sorts: when I tell you that sheer panels are fashionable this season, don't get too excited. Fashion has adopted the sheer panel, but not in the peekaboo sense. In fact, the purpose of sheer on this season's clothes is to add textural interest in a minimalist way, and to bring lightness and breathability to heavy fabrics.

The logic behind fashion's use of sheer is as follows. A simple top such as the Zara one I'm wearing here needs something to catch your eye in store. A bit of a wink. Fifteen years ago, someone would have bought in a job lot of velvet ribbon and jazzed it up that way. Five years ago it would have had a row of brass studs glued on in the style of epaulettes. This summer, instead of decorative interest being added on top, that decorative interest is injected through the fabric being stripped down.

The clean-and-serene tone of sheer when used like this is underscored by shape and colours. There is a world of difference between a white top with a postbox-shaped sheer panel, and a red dress with a heart-shaped sheer panel. And, of course, there is the matter of what exactly you are exposing. This is at your discretion, with discretion being the key word. If fashionability is your aim, this is a trend best worn clean-cut, in all senses.

• Jess wears top, £29.99, and trousers, £35.99, both zara.com. Heels, £100, ninewest.co.uk.

Styling: Melanie Wilkinson. Hair and makeup: Dani Richardson using Nars