The fashion factor: The fashion secrets behind the X Factor

Daniel's ginger hair, Diana's floaty frocks... Carola Long goes backstage at Britain's favourite talent show to uncover their makeover secrets

When The X Factor's familiar opening music starts at about 7.30pm every Saturday, millions of people across the country will be sprucing themselves up for a night out, using the show as a soundtrack to the blending of blusher, or the application of hair gel. For the contestants, however, the ritual of dressing up begins much earlier: at about 9am in a shiny, white wardrobe trailer that resembles a huge fridge, parked inside the stark concrete complex of Fountain Studios in Wembley. This is where the hit show, hailed as one of the saviours of Saturday night television, is filmed.

At the heart of the X Factor formula is the makeover. It would never attract audiences of around 10 million without the fantastic wardrobes, because it needs the sartorial rollercoasters of the "before and after" to heighten the emotional ones so frequently invoked by the contestants. It needs the glitz, the glamour and the "water-cooler moments", as head stylist Faye Sawyer describes the sequinned suit and fur coat that finalist Rhydian Roberts wore last series. Accordingly, the wardrobe trailer is where the contestants come to be transformed, or, as someone immune to The X Factor's cheesy charms might see it, the products in the dream factory come to be packaged.

Inside the trailer, Sawyer, dressed in a sexy but authoritative fitted black dress with a gold chain necklace, heads a team of stylists and seamstresses who are variously engaged in sewing sequins on to a nautical hat and crystals on to a dress (you can never have too much bling on television, apparently), helping the contestants into their outfits, and ironing. Sawyer has recruited three extra people today because the contestants are performing their charity cover single, "Hero", and this demands a quick costume change. "I don't really see how we can get 13 people changed in three minutes, 40 seconds," she says, anxiously, "you'll have to start undressing the minute you come off stage." Styling a contestant such as Austin Drage looks about as easy as dressing a jumping bean. He bounces about the trailer, waving his ringing mobile, and tells me, whilst stripped down to his boxers to reveal a tattoo of a pair of outspread wings across his shoulder blade, to "stop writing and start taking some pictures".

Up until the mid-afternoon dress rehearsal, all the contestants will come into the wardrobe trailer, as well as the hair and make-up rooms, to be squeezed, laced or zipped into their stage outfits. Today, the garments on the rails are for Week 3's "big band" theme, which facilitates the kind of show-stopping, brassy glamour The X Factor thrives on. Think satin, big hair and sequins – and that's just the boys. Simon Cowell described 17-year-old contestant Diana Vickers, who has a distinctive voice, as "the singing version of Marmite – you either love it or hate it", and the same could be said of the ensembles on the show. Most people see genuine flashbulb-popping glamour, some camp razzmatazz, while fans of edgy clothes might apply Louis Walsh's acerbic verdict on ejected girl band Bad Lashes – that they looked like "a bunch of hairdressers" – to many of the contestants. Avant-garde fashion this is not.

"I do sometimes want to do something a bit edgier," said stylist Faye Sawyer, as I accompanied her on a pre-show shopping mission to Selfridges and Topshop earlier in the week, "but then I often think, 'are they really going to be able to work that, or will it overpower them?' The mark of a really good stylist is making sure that the clothes don't wear the people, because then that will make them really uncomfortable."

For every girl such as Diana, who is young and fashion-conscious, or Ruth Lorenzo, with her impressive curves, there is someone such as Daniel Evans. Louis Walsh might have been overly harsh when he compared him to Ricky Gervais, but at 38 he isn't obvious teen heart-throb material. "I'm secretly loving all this makeover stuff," he confides in the trailer, plastered in the deepest of orange foundations. "It's nice having suits made for you when you are used to shopping in Matalan, Primark and Tesco." He's also had his eyelashes and hair dyed, although the latter process went slightly wrong and left him with a gingery Jaffa Cake shade. The teeth whitening didn't go so well, either. As if to shore up his "everyman" credentials, Daniel found it so hard to resist having a nice cup of tea after the treatment that he ignored the rule of no dark liquids for 24 hours, and scuppered the dazzling effect. All the contestants have their teeth whitened – something Sawyer sees not as vanity, but a process to prepare for performing, and instil confidence – "they are singers, and the camera focuses on the mouth," she says. That other X Factor stereotype, fake tan, has been less prominent this year, to the relief of make-up artist Adam De Cruz. "Last year, we had some real fake-tan addicts, who even declared themselves "tanorexics". Hope were too orange, even under the lights."

Perhaps the toning-down of the fake tan symbolises the way the clothes have become more sophisticated over several series. Ellie Crompton, style editor of Heat magazine, certainly thinks that people are taking more notice of X Factor fashion. "This series, our coverage has filtered through from the features pages into fashion." She says, "the clothes are definitely better, and having fashion-conscious judges has helped. I can see a bit of a Cheryl [Cole] influence on Diana: she has the same hippie-ish look, but now it's more polished boho." Crompton says that Cheryl has gone from a "classic Wag" to a more pared-down, glossy look. "Diana also captures people's imaginations, because she is a bit ethereal and different but not too off the wall."

Loitering Bambi-like outside the make-up room, Diana says that the stylists "have got me down to a tee. I hoped they would take my look and make it better, and they have." Diana's signature messy hair makes her stand out on television, where the hairdryer is king. "I started backcombing my hair aged 11," she says, "I disowned my brush and it's gradually got bigger."

Judge Dannii Minogue agrees that "it's really important that the contestants project a unique style. Faye Sawyer is awesome at working with them to highlight their best features."

Crompton says, "the magazine gets a lot of readers asking where they can buy something the girls in the show have worn," and that curiosity can now be satisfied by the new fashion area of the X Factor website. So far, the site has received more than 1,500 emails about fashion, and reveals that the contestants wear a perhaps surprising number of designer outfits mixed with the high-street names. The naval-inspired micro-mini that Alexandra wore for the big band-themed night was a heavily customised Alexander McQueen dress, while fellow British designers Matthew Williamson, Alice Temperley and Julien Macdonald have also featured. Sawyer also commissions a lot of bespoke tailoring by British labels such as Savile Row tailor Richard Anderson and Antony Price, who made suits for Bryan Ferry.

Sawyer finds out the themes for the next week's show on the Sunday before, after which she and her team dash around begging, borrowing or buying clothes and accessories, as well as back-up outfits. Minogue, who works with Sawyer on the contestants she mentors, says "it takes a few weeks with some of them to get it right, but we are always up against time pressure with their availability between rehearsals."

Sawyer says the rapid turnaround means that she has "done a few things that weren't great", such as Girlband in the first week. "I've styled Sophie Ellis-Bextor and I was going for something similarly ironic, with an Eighties pop edge. Unfortunately, the bright jewel colours made them look like Quality Street and it translated really badly on set." Similarly, the red, green and orange sequinned lining to boy band JLS's jackets in Week 3 made them look like flashers standing under traffic lights. However, as with the Oscars, or any red-carpet event, the fashion wouldn't be nearly as engaging if it were perfect every time. The misses make the hits all the sweeter.

Rachel Hylton's first two outfits – a boxy trouser suit and a gold lamé jacket – missed the mark, but when she sees her big-band outfit in the trailer, it is love at first sight. "I love it, I love it!" she cries, hugging the green silk ballgown on the rail. Later she gives the performance of the night. As her mentor, Dannii Minogue, says of the contestants, "they project with more conviction if they look like stars".