British children know David Walliams??? as the author of some of their favourite books, as well as the tall, daffy judge on the TV show Britain's Got Talent. But to their parents he will forever be Emily Howard, the transvestite from the hit comedy series Little Britain whose shrill refrain - "I'm a laydee!" - became one of the most parroted catchphrases of the noughties.
Walliams admits it can be tricky when he has to cater for both his constituencies: young readers aged seven to 12 and adults hoping for a reprise of the show that made him famous. On a recent visit to a school, a boy asked how he met Simon Cowell, the straight man to the high-camp persona Walliams deploys on Britain's Got Talent. "On Grindr" was the first answer that popped into his head. It was a good joke but unsuitable for a room of children. "You have to edit yourself as you go along," he says, "because you don't want to drag them [children] into the adult world unnecessarily."
That doesn't mean young readers can't be challenged or deal with "grown-up" issues. That belief underpins all of Walliams' children's books - 10 and counting - and helps explain their staggering popularity and the frequency with which reviewers compare him to Roald Dahl.
Walliams, who became a devout fan of the British author after "devouring" a copy of Charlie and the Chocolate Factory at the age of 11, is clearly uncomfortable being anointed as Dahl's successor. He has made it clear that he does not consider himself in the same league. No one is, he argues. "It's a nice thing to put on a book cover. But beyond that I don't really think it means anything."
Walliams hatched the idea of writing a children's book in the aftermath of the third and final series of Little Britain. One day he received a photograph from an 11-year-old boy - a fan of the show - who had been inspired by Emily Howard to wear a dress to his school's costume day. Walliams had worn his first dress at a similar age, frocking up for a school play at his all-male grammar school in Reigate, a commuter town on the southern outskirts of London. "I began to wonder what would happen if a boy decided to go to school in a dress," he says. "It's one thing if it's fancy dress, but another thing if it's something he just wanted to do."
The result was The Boy in the Dress, his 2008 debut. It was illustrated by Quentin Blake - Dahl's long time collaborator - and told the story of Dennis, a 12-year-old boy who decides to wear a sparkly dress to school, not as a joke, but because it's beautiful and feels good. The book is compassionate and includes a cast of great characters and tons of laugh-out-loud jokes, some of them scatological. The Times praised its espousal of "freedom and tolerance". To young readers it was simply a great yarn that combined sequins, soccer and a stupid headmaster.
The book's success set Walliams on the road to becoming a publishing phenomenon. Mr Stink, Billionaire Boy, Gangsta Granny and six others followed at the rate of one a year. His global sales now total 20 million - 1 million of them in Australia. He has muscled his way past the likes of J.K. Rowling and Stephenie Meyer to take up what seems like permanent residence at the top of the bestseller lists.
Given its boundary-pushing topic, The Boy in the Dress provoked little controversy. The biggest ripple occurred in Australia a few months ago when its appearance in a supermarket catalogue at the height of the debate on same-sex marriage provoked angry comments on social media from those who accused it of "pushing social agendas". Walliams responded quickly, saying that he had written the book to change the way people think and feel about the subject, adding "???hard to believe this is 2017".
He knows, of course, that acceptance takes time. His effeminacy has made him the target of bullies since the days when he pretended to be Wonder Woman in the school playground. Speculation about his sexuality is something of a national obsession in Britain. He is, surely, the only high-profile male guest to be asked point blank on the BBC show Desert Island Discs: "Have you ever had a relationship with a man?" His answer is always the same. He is attracted to women, has never had a relationship with a man, but wouldn't rule out having one if he fell in love. You might think his candour would stop the tittle-tattle, but it hasn't. Despite the small army of nubiles he dated as a bachelor and a five-year marriage to the Dutch model Lara Stone that produced his son, Alfred, but ended in divorce last year, many people simply refuse to accept he isn't gay. "I'm camp, I've always been camp," he says. "That's who I am."
Walliams takes pride in the way Little Britain and his first book helped bring topics such as sexuality and cross-dressing into the mainstream. Emily Howard and Dafydd Thomas (aka "the only gay in the village") were "celebrating difference", he says and trying to break down barriers via "visibility". Not that the battle is won. "When I go into schools and tell kids the inspiration for my first book was "what" would happen if a boy decided to go to school in a dress', a lot of them still giggle," he says. "So it's still a difficult or unusual subject for some people."
The recent publication of his 10th book, Bad Dad - a tale of fast cars, scary criminals and the bond between a father and son - feels like a milestone, he admits. "Writing felt like a second career at first. I'd achieved success with Matt [Lucas, his Little Britain co-star] and writing felt like an offshoot in a way. But it's not like that any more because it has completely taken over my life."
He is not exaggerating. As well as writing a book a year he reads the popular audio books and co-writes screenplays for the movies based on the books. The latest film, an adaptation of his eighth tome Grandpa's Great Escape, stars Jennifer Saunders, Tom Courtenay and er, David Walliams. There are stage productions and rumours of an animation. He enjoys reading to children in classrooms and celebrated World Book Day in 2015 by using a helicopter to visit six schools in a day.
When I ask, at the age of 46, he now considers himself primarily a writer, I sense him bristle. "Yeah, I'd say so, but I was a writer before. People might think that Little Britain was written by pixies and elves, but that's what Matt and I were doing most of the time - the writing takes a lot more time than the performing. For some reason people don't see television writing, certainly not sketch writing, in the same way as other writing."
He continues to write and perform comedy, but so far none of his post-Little Britain ventures - the budget airline spoof Come Fly Me, for example, or the classroom sitcom Big School - have enjoyed the lightning-in-a-bottle success of the show that made him famous. Walliams is experienced enough to take setbacks in his stride. "There are things I'm satisfied with and some things I'm not," he says with a shrug. "You hope you're improving and the next thing will be better."
Not all his energy is devoted to making people laugh. His long-distance swims - he has conquered the English Channel, the Strait of Gibraltar and the 225-kilometre length of the River Thames - have raised millions of pounds for charity and earned him widespread admiration even among those unmoved by his comedy.
Given his crazy workload it comes as no surprise to learn he considers himself "driven, organised and keen to get things done". "I'm at a point in my life where I'm successful and some people know who I am and there are lots of opportunities. I don't want to squander them." You can understand how all this focus and drive might have caused friction with Lucas who is described in Walliams' startlingly candid 2012 autobiography, Camp David, as a brilliant man with a less-than-dynamic work ethic. To be fair, the book is even harsher on its author who admits to bouts of suicidal self-loathing, sex addiction and a need to be loved by everyone he meets.
Walliams knows there's a thin line between seizing every opportunity and biting off more than he can chew. "Sometimes I think I do too much," he says. "You can definitely appear on screen too much. That's something that you need to consider because people can get bored with you. It's happened a few times in my life and I've regretted it."
It is tempting - irresistible, perhaps - to see parts of the books as autobiographical. As a camp schoolboy Walliams was a natural target for bullies. So are many of his young protagonists who also experience isolation, loneliness and emotional and financial deprivation.
A recurring theme is the relationship between fathers and sons. Walliams spent years trying to win the affection and approval of his own dad Peter, an engineer who died of cancer in 2008. He seems to believe he failed. But Bad Dad paints a touching picture of a man enjoying a tender relationship with his son. "It's a kind of wish fulfilment isn't it," he says when I raise the subject. "The books might not be autobiographical, but they can't help being personal. You can't help pouring yourself and your experiences into them and it comes out in lots of different ways - conscious and subconscious." He pauses. "It would be bizarre if it didn't really."
His children's books have earned him a fortune - ??7 million in 2014 alone - but it is clear they mean much more to him than that. "I think of writing a book as like trying to remember a film you haven't seen," he says. "Although it's a solitary process it feels exciting. At the end of the day you're often looking forward to getting up the next day and spending time with these imaginary characters that become like friends."
And despite all his success, he knows he has more to achieve. "I think the real test with my work will be whether it carries on to another generation," he says. "Roald Dahl wrote some of his books over 50 years ago and three or four generations have loved them. If one day someone comes up to me and says 'I read your book when I was a kid and now I'm reading it to my child', then I'll know I've made it as a children's writer."
The Wonderful World of Walliams will be at the Riverside Theatres, Parramatta, on December 8 and at the City Recital Hall, Sydney, on December 9.