David Walliams on Billionaire Boy, growing up... and on wanting to be remembered "for looking great in a bikini"

Fast-forward to this Christmas. A centrepiece of the BBC1 schedules is an hour-long adaptation of Walliams’s bestselling children’s novel, Billionaire Boy. The plot revolves around the troubles of Joe Spud, the richest lad in the coun- try, whose life is being ruined by the vast fortune his father has made out of – you’re ahead of me here, I’m sure – toilet paper. “Bum Fresh” has taken the world by storm and bought Joe anything he’d ever wanted, except friends. It’s dark, funny and archly lavatorial; kids love it.

It’s a morality tale, of course. Joe only finds happiness when he can put his money, er, behind him (it’s catching). You wondered how Walliams dreams up all this stuff; now you know.

Walliams, 44, isn’t a billionaire himself – yet – but he’s well on the way. Little Britain, the comedy sketch show he wrote and performed with Matt Lucas, was hugely successful and their stage show, Little Britain Live, has played at the biggest arenas in the country. He’s the fey foil to Simon Cowell as a judge on Britain’s Got Talent. On top of that, he’s the fastest-selling children’s author in the land. He’s sold more than four million books, several of which have been turned, like Billionaire Boy, into television specials. I really liked him myself until the grandchildren wanted Gangsta Granny played for the 57th time on the school run and something inside me snapped.

The way he tells it, it’s simple. You just have to think yourself back to your own childhood and what you would have liked to read. “Fortunately,” he says, “I am very immature.

“They want funny stories,” he elaborates, “scary and a bit forbidden. Books you’d read under the covers with a torch, and maybe get into trouble for reading.” No wonder he is endlessly compared with Roald Dahl – “really flattering for me, not so flattering for him”.

In the flesh, he’s groomed and glossy; immaculately barbered with shiny manicured nails, handmade-looking boots of Cordovan leather and the kind of understated gold watch that’s so breathtakingly expensive they tell you it’s not really for you, you’re keeping it in trust for your heirs. He’s easy, in a slightly wary way; thoughtful and very polite.

He reckons there’s quite a bit of himself in Joe Spud. “Joe’s short, fat and unhappy,” he says. “I was tall, fat and unhappy.” At Reigate Grammar, a fee-paying school in Surrey, they called him Daphne, “because I was so effeminate. I felt very alone and isolated.” He learnt to turn it into a joke and then become part of it. “That way, I won.” His epiphany came when he was cast as a queen in a school operetta and got lots of laughs, he’s still not quite sure how. “I got this incredible feeling of power, and suddenly felt in control of something. I wanted that experience over and over again.”

Much of his comedy involves the ambiguities of sex and for a long time the tabloids obsessed about how ambiguous his own sex life was. On the one hand there was his strenuous, and rather public, pursuit of a string of glamorous women followed by marriage to Lara Stone, a famously leggy Dutch model (they divorced earlier this year). On the other, he’s quoted as saying he’s “70 per cent straight”.

In fact, he sees himself as camp, not gay, and when asked straight out if he could ever see himself in a serious relationship with a man, bluntly answers, “No.”

Campery, as he calls it, has a rich tradition in Britain, from the music halls through the Carry On films right through to today’s chat-show hosts. “All of
them are camp,” he says. “Graham Norton, Paul O’Grady, Alan Carr, even Jonathan Ross. He’s pretty camp, the other three are gay and camp. We like it because it’s playful and fun.”

His particular hero – he calls him his “obsession” – is Frankie Howerd. He even played Howerd in the BBC4 drama Rather You Than Me.

There are interesting parallels. Both changed their names to be more distinctive (Walliams was Williams; Howerd was Howard). Both pushed the boundaries of camp sexual innuendo to breaking point – though Howerd was a promiscuous homosexual; he even groped me backstage at Comic Relief. Both fought long and hard against depression.

Walliams has been diagnosed bipolar and has spoken of trying to hang himself aged 12, taking an overdose in his teens and slitting his wrists in his 30s. “Now, I have learnt a lot more how to recognise and pre-empt it; do things to distract myself,” he says. Nonetheless he caused a stir on Desert Island Discs in 2009 by choosing, as his “luxury”, a gun, telling host Kirsty Young, “If I really start hating it, I can shoot myself.”

Back on the mainland, he’s busier than ever – reinventing the sketch show this Christmas for BBC1 with a new programme called Walliams and Friend, the friend being Joanna Lumley. They’ve been trying the sketches out in front of 50 people in the Hen and Chickens pub in Islington, north London.

In the way out of the hotel where we’ve been talking we run into Barbara Windsor, the pocket-sized National Treasure and Carry On queen. It’s a sketch in itself. He’s huge – 6ft 4in. She’s smaller than tiny. They rush into a luvvie embrace that for a moment leaves him clutching empty air a few feet above her head and her hugging his kneecaps.

Before he leaves I ask how he would best like to be remembered – meaning as a comedian or an author? “For looking great in a bikini.”