London calling: Justin Thornton and Thea Bregazzi, whose label Preen is celebrating its 20th anniversary (Photo:formal dresses online)

Like many Remain voters, fashion designer Thea Bregazzi felt pretty emotional on 24 June. She’d woken up to the Brexit news and everything was in turmoil. Her seven-year-old daughter Fauve was upset and asking questions so Thea turned on Newsround in the hope that CBBC could provide answers while she pulled herself together.

“Mummy, look, she’s wearing your dress,” called Fauve from in front of the TV. And she was. As David Cameron announced his resignation, Samantha Cameron stood by his side wearing a resort 2015 dress by Preen, the label Thea runs with her husband Justin Thornton. That was the picture that dominated the international press: David at the lectern, with Samantha downcast but elegant in her beautiful dress, standing slightly removed from the spotlight, but impossible to ignore.

“So, you know,” says Thea, with a rueful chuckle. “Every cloud has a silver lining.”

Preen isn’t the most obvious name for the British label created by Justin and Thea. The word has a sense of vanity or self-aggrandisement that is absent from the designers’ attitude. Though their west London studio has all the expected accoutrements of a fashion brand – bustling assistants, models’ photographs on the walls, nice wooden floors and lots of flowers – Justin and Thea are not very fashion. They’re funny and friendly. They’re like the couple you’re really pleased to bump into on the school run. They could be new characters on the relaunchedCold Feet.

“We’ve never been the next big thing,” says Justin cheerfully, making sure everybody who wants one has a cup of tea.

As the label celebrates its 20th anniversary this year, it’s safe to say they never will be. But that doesn’t mean that Preen isn’t an important part of British design. Even if you’re not familiar with the Preen name, you know their work. A red carpet’s worth of celebrities have worn their clothes – including Beyoncé, Alexa Chung and Scarlett Johansson – but Preen’s speciality is creating glamorous clothes for grown ups. Jennifer Lopez and Christy Turlington are fans. Michelle Obama wears Preen for public appearances. (“We got invited to the White House to meet her! All we do is design frocks and we went to the White House!”)

While many designers like to wax lyrical about inspiration, Justin and Thea are also refreshingly honest about what makes clothes stand out these days and particularly the effect of celebrity fans. Perhaps this is why Preen is a commercial success, despite being one of the UK’s few completely independent fashion labels.

“When we design, we think about the way people are working and living, what’s going on,” says Thea. “I’m very interested in why certain people want to wear certain styles at certain times. It’s all wound up with culture, politics, everything’s in the mix.”

This process led to the creation of the Power dress in 2006. The tight, structured dress was inspired by the 90s supermodels – real women compared to the scrappy waifs who were seen on the catwalks back then – and it was a huge hit, worn by everyone from Cheryl Cole to Rihanna.

“We loved it when Amy Winehouse wore it because she was such a London girl – someone who felt part of our world,” says Thea. “But when Gwyneth Paltrow wore it to the Ironman premiere in 2008, sales went through the roof. That event was the big reveal after she’d started the Tracy Anderson workout. Everyone went: “‘Oooh!’ That was a real moment.”

The new ways in which fashion is viewed and sold even affects how the duo design their collections. “We photograph the clothes all the time so we can see how they look on the phone,” says Justin. “All of our biggest clients are on Instagram so we design things that will photograph well and look good as a static image.”

“We used to be all about black and grey, but that doesn’t sell online,” says Thea, wistfully. “If you do black now, you have to add a graphic element to grab attention.”

Even the way the clothes are first unveiled has changed since Preen first opened its doors. The general public now watch the catwalk show and see the looks from the collection at pretty much the same time as the fashion editors and buyers.

“The customer used to just see what was in the shops, but now they’ve seen showpieces on the runway and that’s what they want. Those clothes are hard to make, so the fear is that designers will start creating blander clothes for the catwalk show, things that are easy to produce. I don’t want that to happen to us. But now we’re producing four collections a year for Preen on top of our other commitments, we’re going as fast as we can. Something will have to give, won’t it?”

They both look a bit worried, which is understandable. They’ve come a long way during their fashion careers, but so has the industry they work in. The landscape is unrecognisable.

The couple first met as teenagers on an art foundation course on the Isle of Man, where they both grew up. The fashion industry wasn’t a big part of Manx culture, but they started at college just as the last significant shift in fashion culture occurred. “Grunge was happening, Corinne Day’s photography took off, there wasi-D magazine… fashion stopped being simply about sophisticated Italian labels when we were at college. It became something that our friends wore, something accessible.” They moved to London in the 1990s after university, and set up Preen as a shop in Portobello. The area was the creative hub of the time and everyone used to hang out there.

“We were looking for a studio, but then a friend suggested getting a shop because we could earn our rent back by selling stock. The first week we opened Cher and Janet Jackson came in and we thought: ‘Oh God, this is great!’ We thought it would always be like that which, of course, it wasn’t, but it was fun and creative.”

A lot of the clothes were made at their flat or out the back of the shop. They tried stuff out for a laugh to see what people would buy. One of their first design hits was drainpipe trousers, the skinny shape that came to define the following decade. Kate Moss used to come in and pick up a couple of pairs at a time. Eventually they did a catwalk show and paid the models in clothes.

“We would not have survived if we’d come out of college and had to be slick from the start. Nobody at London Fashion Week really knew what they were doing back then,” says Thea. “Other people in the industry would point out what you were doing wrong and help out.”

The Preen shows moved from London to New York between 2008 and 2012, because at that time no one took London Fashion Week very seriously.

“By the third season of showing there, we’d doubled our business internationally,” says Justin. “Plus, we had a great time. Londoners are always too cool to say what they really think. Americans are positive, positive, positive. They were, like, ‘We LOVE you guys!’”

But Preen is at heart a London label and the collections have been back in the British capital since 2012. “At the first show back there was real warmth from the London crowd,” says Justin.

“Though that lasted about 10 minutes,” hoots Thea.

Their 20th anniversary show took place last week without, as Justin puts it “a lot of razzmatazz”. “We’re just pleased that we’ve managed to stay at this level for this long, making clothes that people really like. It’s great that we’ve been bloody-minded enough to do it.”

They’re not planning any big events to mark their first two decades, which isn’t a surprise. That’s the Preen way. Not the centre of attention – standing slightly removed from the spotlight, but impossible to ignore.Read more at:bridesmaid dresses