A Slice of Britain: Frenetic, kinetic, absurd. The world behind the scenes of designer Kinder Aggugini's show at Somerset House is barely controlled chaos until the models hit the catwalk – with perfect poise

Out there, the fashion pack in their seats, all is calm. Back here – behind the scenes before Italian-born Kinder Aggugini's show – is barely organised chaos.

A clique of models wear nothing but yellow cloth over their heads and flesh-coloured knickers. This is not some hideous, avant-garde stab at haute couture, merely a desperate attempt to protect the military-inspired jackets, dresses, and cashmere-cotton shirts in Aggugini's new collection from the girls' dramatic, spray-on black hair colouring.

The designer, who worked for John Galliano and Vivienne Westwood before launching his own debut collection a year ago, is an island of calm. All around him, models, make-up artists, production managers and dressers are melting down in a kind of China Syndrome on heels.

This year's collection is inspired by the Napoleonic era. One side of the small room is devoted to turning fresh-faced teenagers in jeans into beauties to rival the French emperor's lover, Josephine. They sit, staring blankly, in front of rows of mirrors framed with light bulbs, dressing tables heaving with hairbands, pins and sprays.

As strident as the teens are silent, heavily tattooed head hairstylist Malcolm Edwards spurs on his team as they battle to get 19 models catwalk-ready. "I'm walking around like Adolf Hitler here," laughs the 41-year-old. His team members swarm and yank hair brushes ever more violently, glancing at photos pinned to the wall showing the dramatic, black up-do they must re-create.

"I saw the clothes two days ago, and then got the idea in my head: the idea is a rose in a forest full of thorns," he says. A brilliant concept – 18 of the 19 models wearing their hair black and up, leaving just one redhead – which is torpedoed just five minutes before the show is set to start, when the last model to arrive refuses, point blank, to have her blond hair sprayed black. Amazingly, Edwards, instead of going all "Hitler", is philosophical: "You can make requests at Fashion Week, but you might not get it: the poor cows have probably been up since three."

By his side, a red-haired model chats on the phone, apparently oblivious to the make-up artist dotting concealer on her invisible blemishes. "Some of the girls are quite young," says model Kelsy Van Mook, 18. "I think you really have to love what you do. It is an adrenalin rush, but I'm really tired. I did 20 shows in New York, then flew in on the red-eye the night before last to start the shows here."

We only get to hear about models who won't get out of bed without the prospect of thousands of pounds. The reality for the girls starting out is that they can expect about £100 per show, the minimum amount recommended by the British Fashion Council (BFC) and the Association of Model Agents (AMA). In a notoriously fickle industry, the minimum increases for every season a model continues to work.

The girls pretty much ignore a long table bearing rows of bottled water, and bags filled with cereal bars, croissants and orange juice. The Model Health Inquiry set up in 2007, due to fears about "size zero" models, led to a requirement for food and drink to be provided backstage. There are no rules saying the models have to eat it.

Just 45 minutes before the show starts, a member of the 20-strong production team runs through the room, bellowing: "Put down your utensils. Put. Them. DOWN! We need to have a walk-through NOW." Moments later a hurried dress rehearsal of the show – which cost upwards of £12,000 to produce – is in progress.

The models, in black gowns, many of their newly painted heads wrapped in cling film, strut down a catwalk still covered in plastic sheeting. Lighting technicians transform the auditorium from pitch black to eye-searingly bright. Behind, workmen on a stepladder hitch up a sign saying "Kinder Aggugini".

In keeping with the Napoleonic theme, a column bearing a golden eagle has been placed at the end of the catwalk. More trouble: a debate ensues between the production team and a group of photographers who staked out the best spots days ago. While the photographers mill at the end of the catwalk, the room's 500 seats are allocated according to a strict hierarchy: top fashion editors, buyers and VIPs in the coveted front row.

With 68 shows going on at the capital's neoclassical Somerset House, which is playing host to many of London Fashion Week's 200 designers over six days, the schedule is nail-bitingly, nerve-shreddingly tight.

The frenetic, kinetic last-minute preparations, the emergency fixes and changes and alterations, the shouts and hissed instructions take on the air of a battle control room. Then, finally, almost 30 minutes late – respectable in fashion time – the girls head out on to the catwalk to the strains of a Kate Bush remix. Out there, to the studiedly cool audience, it appears co-ordinated and calm.

Behind the scenes, as models step off the catwalk, they sprint – in six-inch heels – rip off their outfit and grab another. Production staff run beside one girl, buttoning up her top until the very second she steps out from behind the screen, while one tearful-looking model is berated for missing her slot completely: she couldn't cram her feet into the standard size-seven shoes all models are given.

Then, almost as soon as it has begun, the show is over. Models slip back into their jeans; make-up artists pack up and the catwalk is cleared – ready for the next show.