Hat trick: How milliner to the stars Philip Treacy gets ahead

His extraordinary creations have adorned everyone from Lady Gaga to the Duchess of Cornwall… How did one man change our minds on headgear? Harriet Walker meets Philip Treacy, the monarch of millinery.

The main road through Battersea is closed when I make my way to meet milliner Philip Treacy in his south London studio, because of the helicopter crash a week earlier. The bridges across the river are all crammed with traffic, and the trains are running a depleted service because of a dusting of snow that has long since turned black on the pavements.

What a relief then, when I am whisked up some stairs on the edge of an industrial estate and into Treacy's workroom, a botanical garden of hats half-finished and half-started, of gleaming wooden 'maquettes' – the blocks from which each style is sculpted – and framed odysseys of his imagination sported in celluloid by royalty both populist and literal, by supermodels, icons and artists.

It is here that all of Treacy's hats are made: the blocks are honed in Paris, but the hats themselves take shape in the workroom. "People talk about no manufacturing in central London," he laughs. "We're the best example of British manufacturing, because we make an intrinsically British product right here, entirely by hand!"

In among feathers of all hues, trims, wisps of straw and handmade floral corsages are several busts, including a neo-classical Artemis with tumbling curls lurking behind a pot plant and a wax rendering that I later find out is the Tussaud's bust of the singer Lady Gaga, given to Treacy, so he can knock her up a titfer wherever she is in the world. Pinned to one wall is a rhapsodic note from her; on the opposite side of the room, a photo of the Prince of Wales and the Duchess of Cornwall on their wedding day, with 'Thanks' scrawled across the bottom.

"Women come into our shop for that ultimate moment in their life," the 45-year-old Treacy says, looking suitably paradisiac himself, resplendent in matching lobster-pink jumper and jeans, a silver thimble on his ring finger. "They're buying a dream. They're buying a moment for themselves. That's what I sell – moments."

He creates them, too. Last September, he took over the Royal Courts of Justice and staged a show during London Fashion Week comprising an all-black ensemble of models wearing hats of his creation with the personal wardrobe of Michael Jackson – just weeks before it was auctioned off. Marking the 20th anniversary of Treacy's first London show, and his 22nd year in the industry, a sunset yellow-coloured smiley hat was paired with the red leather jacket from "Thriller"; a rotary-powered Neverland fairground scene perched atop the brow of a model in an 'MJ' emblazoned baseball jacket; a bejewelled, flower-encrusted mask worn with the metallic military-wear from the 1996 History tour, all marching to a soundtrack of Off the Wall-era classics and presided over by none other than Gaga herself, who – clad in a hot pink full-length veil – kicked off proceedings with the announcement that Treacy was the "best milliner in the world".

"I was mortified in case people thought I'd put her up to it," he says hastily at the memory. "She said, 'I'll say what I think, you can trust me'. She understands where I'm coming from. I'm not trying to rule the world, I'm just trying to make hats. I'm trying to make hats that will bring a future to an industry that needs help.

"People are always trying to kill them off," he continues. "Saying, 'Nobody wears them' or whatever. But hats are attached to special moments in people's lives – weddings, or the races. In difficult times, people still get married, they still want to look their best. And there's a whole new generation of people interested in hats – the age group of the customer when I started was certainly much older, and now it's not. So that's slightly killed that theory."

In truth, Treacy has never been busier: the past few years have cemented him as a household name, after 36 commissions for the Royal Wedding in 2011 alone (including Victoria Beckham and an unfortunately mocked looking-glass number for Princess Beatrice, which raised £81,000 when auctioned for charity on eBay), which saw him working solidly for two weeks without a break to ensure all guests were happy, and no styles were replicated or egos overlapped. Months later, he created a headdress for Madonna's appearance at the Superbowl, and has made for Lady Gaga pieces that have been photographed to within an inch of their lives – there have been a fair few of them, given that the flamboyant superstar rarely lets her sartorial guard down.

"People are dressing like stars," he says, "which is kind of fantastic. Last night I was watching TV and it's one channel after another of reality shows – whether it's about a house or a lifestyle or dining. I think that's created a whole sense of 'Because I'm worth it'. And it filters into how people are dressing. Certainly people like Gaga have introduced a new type of hat-wearing."

Treacy's hats have always been elaborate, constructed and surreal – from the space-age hennins and face-framing curlicues that he has made for the singer and his long-term friend Grace Jones, to the Dali-esque galleons, Pop Art and trompe l'oeils favoured by the style set, and in particular the late fashion editor Isabella Blow. It was she who initiated Treacy into the industry, advising and propping him up during his post-grad days, just as she did his contemporary Alexander McQueen.

"Isabella helped hats enormously because she always wore them. She'd say, 'When am I going to an event? I'm just going to work'. She led the way for people like Lady Gaga. I remind people: that is what Isabella looked like – fearless. Isabella wore hats and I made them. We weren't a horse-and-cart act, but in a way it was the perfect combination."

Born in Ahascragh, County Galway, Treacy was always drawn to the fabulousness of formal occasions. As a child he would attend weddings uninvited to ogle the well-turned-out guests. "It's that moment when you see someone looking just right," he explains. "That's what makes designers go on, because you're making your version of beautiful.

"I was interested in fashion and clothing – I didn't know what fashion or design was, but I was good at it. Working with my hands: fundamentally, that is my talent. I can make something out of nothing and people dream about it."

Having begun his training in Dublin, it was while Treacy was studying millinery at London's Royal College of Art that he was commissioned to create a hat for a Tatler shoot, which was where he bumped into Blow.

"We were very close," he remembers. "She was quite motherly. She thought it was completely normal that I could sit here for a week just making one hat. She didn't tell me to get a grip, she encouraged me. To encourage a young person just starting out is the most important thing in the world."

Within six months of starting the course, Treacy found himself in Chanel's Paris showrooms, designing headgear for Karl Lagerfeld's next show. He would also go on to make hats for the Givenchy couture catwalk (at the time overseen by Alexander McQueen) as well as for Valentino, Donna Karan and eventually for McQueen's own label, too. In 2000, Treacy was the first milliner to be invited by Paris's Chambre Syndicale to show during couture week.

"I was so shy," he says. "I found it really difficult to hold a conversation – all I could do was make a hat. The first time at Chanel, I found myself in front of a desk with Karl Lagerfeld, Anna Wintour, Grace Coddington and Liz Tilberis, and on the other side Herb Ritts and Helmut Newton. And Lagerfeld said, 'OK, Philip, what shall we do now?'."

A new book out this month celebrates these backroom moments of Treacy's career, no less striking than the headpieces he creates but perhaps less immediately glittering. Captured on film, Polaroid and, more recently, digital camera by photographer Kevin Davies, with whom Treacy has worked since an American Vogue portrait in 1991, they tell the unseen stories behind all of the "moments", from Treacy fitting Grace Jones for a shoot in the middle of the night to him ironing Naomi Campbell's dress before heading to Ascot.

"I was immediately struck by Philip's personality," says Davies. "Unlike a lot of subjects he asked endless questions. I found his work intriguing, and wanted to know more."

"There's a massive déjà vu attached to my working life," Treacy says, "because I was the one looking at Top of the Pops with these extraordinary people, and suddenly they're coming through the door. Grace Jones, Jerry Hall, Armani, Irving Penn, Karl Lagerfeld – I didn't set out thinking 'I want to meet that person', I started out thinking, 'I'll never meet that person'.

"But fashion people are fighters, because they can come from nowhere and find themselves in the middle of it all."

Surrounded as he is by exotic blooms of boaters and bonnets, that statement is fairly accurate. But, while he might be in the middle of things right here, Philip Treacy is also a man at the top of his game.

'Philip Treacy' by Kevin Davies, £39.95, Phaidon 2013, phaidon.com