Tiffany Taylor travels near and far for inspiration for her latest bras. The result is often a triumph of aesthetics and engineering

Tiffany Taylor carries bras in her handbag and sometimes, when she forgets herself, they dangle from her hand. "Occasionally I'll walk into the London underground and catch people looking at me oddly and I'll realise what I'm holding," she says. "If I ever lost my mobile it would be really embarrassing. Everything on it is about bras – pictures of bras, ideas for bras ..."

Since January, 31-year-old Taylor has helped to boost the assets of a large chunk of middle England in her role as the lingerie and swimwear designer for John Lewis. From next spring, if you buy an own-brand bra from the store, it will have been devised by Taylor.

It's a delicate responsibility. Underwear that will appeal to Everywoman must be attractive, innovative, fashionable and functional. Above all, it must compete with that custodian of female contours, M&S. Small surprise then that, when most of us would spot a striking shoe in a shoe shop or a striking dress on a fellow commuter, Taylor will see a bra – maybe an inspiring pattern for one on a shoe heel or a glimpse of an unusual strap beneath the dress.

"To the average person, one lace bra looks much like another lace bra, so it's the tiny detail that counts," she says. "Part of the fun of design is seeing inspiration in everything."

Canadian-born Taylor, who designs prints and lingerie for other clients alongside John Lewis, grew up wanting to be a fashion designer: "I'd sit in the back of classes sketching dresses. But I always assumed it was more of a fantasy job, like being a princess or a pop star, than reality."

It became closer to reality when she enrolled on a fashion design course at London's Ravensbourne College and it was there, while working on placement with a lingerie designer for Tesco, that she discovered a fascination with underwear. "I've always had a strong scientific and artistic side and there was a tension between the two," she says. "Lingerie is all about engineering and I loved the challenge of reconciling that with the aesthetics of undergarments. It's harder to do something really different with a bra than with a dress because you can't change the basic shape or volume."

Despite – or perhaps because of – the fact that lingerie is hidden from public view Taylor reckons it can express a woman's personality more volubly than clothes: "You buy it because it pleases you, not because you're being dictated to by other people or brands. There's no peer pressure in lingerie, so it can be more of an indulgence."

I'm surprised by this. I've always regarded bras as tedious necessities, like dental floss and petrol. I still rely on the three limp grey strips with which my mother equipped me 15 years ago. Research by Oxfam, however, suggests that women collect bras as lovingly as shoes. The average woman has nine, a third of them unworn, and, according to Taylor, they are investing more money in each garment.

Unbeknown to me, therefore, bra design and technology has been evolving to accommodate the more discerning (and more expansive) customer. "When I started 10 years ago, lingerie was a tiny industry and focused on young flirty wear," Taylor says. "It was assumed that women wanted sexy, aspirational lingerie, but today's women feel far more comfortable in their curves and so are going for the more classic look."

Meanwhile, the curves are growing considerably larger and Taylor, along with other designers, has had to glamorise supports for the fuller figure. "The double D cup is the fastest growing area," she says. "Some of the bras I work with are like helmets. Bigger sizes used to be very functional, designed for older, frumpy women, but now people want them to look attractive."

Developments in moulding and bonding technology have revolutionised her scope. Machines can bond and trim fabrics so smoothly that the lumps and bumps that would once have disfigured a tight-fitting top are eliminated and designers can experiment more freely.

On graduating from college, Taylor launched herself as a freelance designer and Tesco was among the clients that retained her services. She was approached by John Lewis last year via Linkedin, and now freelances for the store three days a week designing lingerie and swimwear for spring 2013.

The design studio is a carnival of colour at the end of long grey corridors in the tall grey tower that is the company's head office. Rails of rainbow-hued fabrics sit beside every desk and the walls behind are patchworked with swatches and fashion photos. "You can tell the changing seasons by the changing colours in the office," says Taylor.

Each designer has their own speciality, from knitwear to accessories, and Taylor's perch is easily identified by the gallery of bras pinned behind it. But when it comes to ideas there is an amiable collaboration between the desks. "If one person uses a particular print, we can all use it," says Taylor. "The kaftan and accessories designer will use the same prints as my swimwear, for instance, and we all have to be aware of which colours and combinations the others are using."

Since new ranges are designed two seasons ahead, Taylor has to predict trends before she can settle to her drawing board. At the start of each season, all the designers gather for a presentation by a trend consultant whose job is to research shopping patterns and shifting cultural influences. "Sometimes there's a movie in production or a TV series – like Coco Before Chanel – that is likely to influence fashion, so you have to be clued up," says Taylor, who is dispatched on two overseas research trips for inspiration at the start of each season.

"I'll look at trends in youthful beachwear in Ibiza, and for the more mature customer Monaco," she says. "I also visit vintage markets in New York and San Francisco, because sometimes you can learn from manufacturing techniques that have died out but might be worth reviving. You have to be ruthless. You can fall in love with the most beautiful garment but it's not right for the range, or you can find a hideous thing that has huge potential."

The root of her inspiration, however, comes from customers. "I normally build on the existing range so you have to understand what's been selling," says Taylor, who will often wait around lingerie departments watching women's reactions and shopping habits.

Once she has completed her research expeditions she makes a collage of swatches and trimmings to illustrate the styles, colours and fabrics she predicts will be in demand in two seasons time and shows it to the store buyers, who add their own feedback: "People think that if you're a designer you just do a little picture from your imagination, but it's all very collaborative work with buyers, merchandisers, suppliers and manufacturers. Next spring is predicted to be lighter, softer colours – so you wouldn't want a purple bra."

She then examines the hundreds of fabric samples sent in by suppliers and, from these, puts together a specific shape. It's in this intricate splicing of fabrics that the expense of a bra lies. There are more than 26 components in the most basic bra, more than any other garment, and over 30 stitching operations are required to assemble them. And although to the untutored eye, most bra and knicker shapes look similar, Taylor says they can be altered in innumerable subtle ways simply by how the seams are positioned and fabrics combined.

Once the contours are decided, she selects trimmings from thousands of samples of lace, threading and bows, sticks the chosen fabric swatches and accompanying trims on to a design board, and shows it to the buyers. After ideas are approved, a sample is run up by the manufacturer and the complex process of fitting – by a technical expert on a series of differently-endowed models – begins. Around 10% of designs are shed at this stage, leaving an average of 20 for the new range.

Swimwear follows womenswear fashions more closely but is as much of a challenge as bras and pants: "The average woman feels out of her comfort zone with so much of herself on display in public, so the costume has to make her feel at ease, while at the same time being sexy and glamorous."

Her job, she says is a consuming passion and her husband has grown immune to a house stuffed with lingerie, and weekends hanging round lingerie shops while she pursues her research. Women, when they discover her profession, tend to share her excitement but, although their underclothes might betray their personality more revealingly than their outerwear, they regard underwear rationally, as a product. Men, however, are another matter.

"They tend to switch off when I tell them what I do, because they associate lingerie with sexuality and their minds start wandering to other areas," she says. "They assume that if you're a lingerie designer you must be thinking about sex all the time!"