Everyone has an opinion on M&S underwear. Too white, too colourful, too plain, too fancy, bras that go grey in the wash and underpants that don’t give Jeremy Paxman enough support. But say what you will about it, you can’t fault the enthusiasm of the people responsible for it. From the head of technology to the buyer, and from the trading director to the designers, the inhabitants of M&S’s lingerie HQ love underwear to a degree that is either spooky or reassuring, depending on your point of view. They can – and believe me, they do – talk for hours about multipack Y-fronts, machine-washable silk and the challenges of building an E-cup bra. Their job is to give us the bodies we think we deserve, and they relish it.

Women have always battled their bodies, and aspired to a certain silhouette. From hideously uncomfortable corsets to the pointy, immobile breasts of the Sixties, we want our underwear variously to smooth, lift, squish and flatten. The 115 people in the bra-bedecked lingerie department at M&S in northwest London do vast amounts of research to work out which bits we want to squish and which to lift. Then they try to give it to us in machine-washable sizes, from teeny to vast.

There is a man whose job it is to trawl the world for the latest ways to knit seam-free tights, and the best gauge of metal to use in bras. There is a trend expert who knows what colour bra we will want in two years’ time, and a technical manager who worries whether we’ll buy it in the right size. There are designers who agonise over the 26 components in the average bra, and every millimetre that can be pared from an E-cup. “It’s a bit of an obsession for me,” admits Soozie Jenkinson, head of design. “I love that we have to know about catwalk fashion, body shape and fabric development. And I love that we appeal to so many different customers.”

Indeed they do. M&S sells more than £650 million of lingerie every year and accounts for around a quarter of the market; one in three women wear M&S underwear, and one in four men. Lingerie is the company’s third-biggest money spinner, after food and womenswear. “That,” as Frances Russell, trading director of lingerie, points out, “is an awful lot of bras.” Twenty million bras, to be exact, in 78 different sizes; and 50 million pairs of knickers, 32 million pairs of men’s underpants and 28 million pairs of tights. “We fit bras on 25,000 women a week,” Russell continues. “That blows me away.”

Gone are the days when women had a white bra, a black bra and a few pairs of pants. These days, it’s all about having a lingerie wardrobe (but then they would say that). Although the bestselling bra colour is white, the drawers of the nation are apparently filling up with a multitude of colourful, embroidered scanties: smooth T-shirt bras, sports bras, the no-VPL knickers that have been flying off the shelves, and bras built for seduction. In the past few years, lingerie has become like clothes, with trends, seasons and directions.

Take knickers: it used to be all about thongs, but now people want Brazilians (a sort of skimpy-but-not-too-skimpy midi style). Most knickers used to start at your waist; now there are 15 styles with waistlines ranging from a couple of centimetres below, to barely decent. Women used to put up with uncomfortable shapewear they could barely breathe in if it made their stomach look flatter. Not any more. “Our research showed that shapewear was seen as old and granny-ish,” says Lisa Joughin, product development

technologist. “When we launched our ultimate Shapewear, sales doubled. We use a type of knitting technology that puts real power in the fabric, so we knit targeted zones: more power in the tummy and down the thigh, and more in the bum area to lift the bottom. It’s not restrictive. It just firms up what you’ve got.”

The result is never going to make men go weak at the knees (Hugh Grant was acting in Bridget Jones’s Diary, OK?) but the fabric is at least soft and breathable and the effects are clearly worth it to millions of women, and not just those in the biggest-selling size 14: they sell a fair few in size 10 as well, to women who simply want a smooth underwear line beneath a tight dress.

There is constant input from the shop floor about what women want: M&S have a market research group that talks to customers every month, focus groups that research possible new pieces, and what they call a “supernet” of around 30 key people from the stores, from managers to bra-fitters, who report back on everything – what’s in store, how it’s laid out, how customers are reacting to it, how new products are going down. “It’s grassroots stuff,” says Frances Russell. “This fitted well, that didn’t, people like this, not that. Obviously we get the sales data, but it’s that raw, intuitive feel for it that we get from them.”

But how much really changes in lingerie? It’s all just knickers, isn’t it? Well, yes, and no. In the same way as fashion isn’t just about keeping you warm, so lingerie isn’t just about keeping you decent. And, as people like buying new things, and retailers have things to sell, so there are trends in lingerie and as many different shapes of knicker as M&S think they can flog. Boy shorts have been the big success story of the past four or five years and, whereas lingerie could once get away with lead times of six to eight months (compared to as little as four weeks for, say, a T-shirt), these days they’re working hard to try to speed things up. “People think, ‘Wow, that low back looks amazing on Jennifer Aniston, that’s the look I want for Christmas.’ We need to provide the right lingerie for that,” says Soozie Jenkinson.

Jennifer Aniston notwithstanding, lingerie is currently having a vintage moment, and celebrating a new focus on waists. From Jenkinson’s point of view, this is a dramatic change. “The natural waist seems almost to have vanished, so women need help from their lingerie to achieve that look. Women want their underwear to help their outerwear look its best.”

They also want to celebrate their curves, which is just as well as we’re all getting curvier. The average bra size goes up by a cup every generation, and the national average is now 36C. Where once we flocked to buy minimiser bras, now, according to technical manager Julia Mercer, “People are celebrating breasts more, and they’re proud of what they’ve got.” Mercer’s shtick is that all breasts are not created equal: put five women with 32Fs in a row, she says, and every single pair will be different, and thus will suit a different bra. It’s not just about the size of the bra, it’s the type. Do you know if your breasts look best in a plunge bra or a balcony one? Moulded or padded? Underwired or seam-free?

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