12.30pm: FOR OUR SECOND MEETING, Alan Cumming arrives wearing a disguise. Naturally, I do not recognise him. Instead, I sit alone at a table in the restaurant, in the Meatpacking District of Manhattan. I wait, and I watch the door. It's early, but the diner slowly fills with a mixture of metropolitan hipsters and old men from nearby warehouses. Twenty minutes pass. Eventually, a slightly frightening-looking man - whose arrival I noted some time before - comes over. "Have you been waiting ages?" he asks agreeably, in a soft Scots accent. "I have."

Cumming is wearing enormous glasses with thick black plastic frames. Since I last saw him, he has had most of his hair shaved off. And he has grown a substantial, Swedish-porno-style moustache. There is a touch of Groucho Marx about the whole get-up, I suggest.

"I thought it was more like Harry Potter, porn star." He says. "I could be the porn version of Harry Potter: with his specs and my moustache."

I point out that this combination represents an impenetrable disguise. He doesn't even need glasses. Is this deliberate?

"I suppose so, yeah. There are some days when you don't feel like being Alan Cumming. You'll do something like that."

And sometimes you forget you're meeting someone who might need to recognise you?

"Oh, yeah," he says, as if this is occurring to him for the first time, and giggles. "That was a bit stupid, I suppose."

THEY KNOW ALAN CUMMING quite well in Manhattan these days. He's lived there since he came to perform in the Broadway production of Cabaret in 1998. His performance as the MC - infamously closing the show by bending over and whipping up his coat to reveal a swastika tattooed on his spotlit buttocks- made him a star in America.

In Britain he's still remembered for his appearance in The High Life - the high-camp trolley-dolly sitcom set on a Scottish airline- as much as his film or classical stage work. But Hollywood has embraced him with an ardour made all the more surprising by Cumming's openness about his bisexuality and his preparedness to say in public almost anything that comes into his head.

"I am the acceptable face of sexual ambiguity," he says. "I'm like a naughty schoolboy- I can get away with stuff, say stuff that's controversial. I giggle a lot and I'm foreign - which is a big thing. I've done lots of heavyweight classy things. And I can dip my finger in trash quite easily."

Having made his mark as Minnie Driver's oleaginous would-be suitor in 1995's Circle of Friends, he continued to avoid lead roles, instead making a series of supporting parts his own: "Pantomime is a big thing in the cultural calendar of my country, you know. So subtlety's not my forte. I think you can be as big as you like as long as you mean it. I really do."

Cumming's appearances are often brief but spectacular. As the lascivious desk clerk ("a flaming queen who's obviously besotted ") fawning over Tom Cruise, he's responsible for the only enjoyable scene in Kubrick's otherwise torpid Eyes Wide Shut. He's great in Emma, and hilarious in both Spy Kids movies. His guest appearance in Sex And The City as Dolce And Gabbana's man in New York, 'O', led to a period in which the character's catchphrase- "We likey!" was quoted at him wherever he went. He's also made some terrible and peculiar choices. In The Flintstones' Viva Rock Vegas, he plays a green alien called the Great Gazoo who spends much of the film flying around in a tiny flying saucer; he's the villain in the Stallone remake of Get Carter; and plays a chimp trainer in the failed simian love story Buddy. But he always gets away with it.

In 2001, Cumming and Jennifer Jason Leigh co-wrote and -directed their own film, the Anniversary Party, and cast some of their friends in it: including Gwyneth Paltrow, Kevin Kline, John C Reilly and Parker Posey. This added to Cumming's already bewildering array of projects, encompassing everything from his not-for-profit theatre production company The Art Party to his role as Nightcrawler in this summer's superhero blockbuster X-Men 2. And now, he's written a novel.

Set in 90s London, 'Tommy's Tale' follows a photographer's assistant through sexual encounters with men and women; through ecstasy, cocaine and ketamine; through crises with his boyfriend and his ex-girlfriend about the need to have children; and, ultimately, into a nervous breakdown. But the book is really a fantasy about something that has long preoccupied Cumming: how, in a world where divorce and parental strife are commonplace, your friends come to replace your family.

When we first meet in London, in December, we talk a lot about the book. Cumming is charming and funny, both flirty and shy. For a man with a reputation for the outrageous, he is more guarded than I had expected. The press are always making painful mistakes about his past, he says, perhaps because before he's been evasive- glossed over things he didn't want people to know. He often deflects questions on sensitive topics simply by trailing off into an entreating 'you know…' - a tactic which works more frequently than it should. At one point, he's about to say 'my next film', hesitates slightly, and then adopts a parody pretentious actor voice to say it. I point out that he's allowed to say things like that: it's his job. "I know," he says. "But it does sound a bit wanky, doesn't it?" He tells me several unprintably scandalous things about Tom Cruise. And a few days later, he calls me to say he would like to meet again: to get a few things straight, and get his story sorted out, once and for all.