Matt Lucas is beside himself. Bursting with pride, he beckons me closer so that he can show me what he's wearing on his scarf. "It's a Blue Peter badge!" he says, beaming.
He's like a big kid, and the same childlike quality has shone through in many of Lucas's most memorable performances - from George Dawes, the outsized baby on Shooting Stars, to the puerile petulance of Vicky Pollard, the childish self-absorption of Daffyd, the only gay in the village, and the egotistical arrested-development of Andy, the pretend wheelchair-user, on Little Britain. So it was an inspired piece of casting to invite Lucas to play the biggest kid of them all, Mr Toad, in Lee Hall's captivating new adaptation of The Wind in the Willows.
In this version of Kenneth Grahame's classic 1908 tale from the riverbank, Toad behaves like a hyperactive child who has overdosed on E numbers. When his more responsible friends, Badger (Bob Hoskins), Ratty (Mark Gatiss) and Mole (Lee Ingleby), try to rein in his car-driving excesses and confine him to Toad Hall, he uses an old playground trick to evade them. Pointing at the ceiling, he distracts them by exclaiming, "Oh, look, a shark!", before dashing off and escaping their clutches. Later, after he and his pals have driven the weasels from Toad Hall, he dons a red quilted smoking jacket and toasts himself with infantile glee: "What fun is life without a bit of showing off?"
Lucas would share that sentiment. In real life, he is modest and measured, with an acute awareness of the pitfalls of fame unusual in such a big star. Once in character, however, he unleashes a riotous alter ego on the world. Wearing a sober dark-red velvet jacket, black trousers and matching shoes - well-polished - he says: "I just like dressing up. I'm quite a preppy, dull dresser in real life. So, appearing on screen as these characters is an outlet for me to be outrageous." However, at the reception after the 32-year-old comic's recent civil-partnership ceremony with the television producer Kevin McGee, he did dress as a flamboyant Ali Baba.
Lucas was delighted that the part of Mr Toad gave him the opportunity to drag up. He has to dress as a washerwoman in the scene where he pulls off a daring escape from jail. "Oh, that was a challenge," deadpans the actor, many of whose most celebrated performances - Vicky Pollard, Marjorie Dawes, Bubbles Devere, Ting Tong - have been as females. "There is clearly no escape from dragging up for me. If I ever play Hamlet, it'll be in a dress!"
For all the cartoonish excesses, Lucas's Toad is a very human character, a spoilt but ultimately adorable kid. "He's vain, maddening and very annoying, but in spite of all that, he has to be likeable," says Lucas. "You have to make him a bit cute and affable. Above all, the audience has to keep forgiving him. Do you remember when you arrived on your first day at nursery, there was always one kid who was far more naughty and confident than you? He'd be running around the classroom pretending to be a car or a plane, and you'd get punch-drunk trying to follow him. He was mischievous and always getting into trouble, but he was ultimately loveable. Well, Toad is exactly the same.
"He starts out with the best intentions, always vowing to be good, but he has a memory like a goldfish. He instantly forgets his promises and starts misbehaving again. He's like a 'trustafarian' who has inherited loads of money but has absolutely no sense of responsibility."
So, does Lucas identify with Toad at all? "He just wants to have fun, and I can totally understand that. He has cast off any sense of obligation and just lives in the moment. He's not shackled, which is, of course, what leads to his downfall. But I couldn't do that. I'd suffer too much guilt."
Lucas says that he was drawn to Mr Toad because it gave him the chance to diversify. "It's the sort of part any performer would kill for. But I also wanted to do it because I felt I had something to prove. People still stop me in the street and say, 'Hi, George Dawes!', so I wanted to show them that there was more to me than that. I'm trying to grow from a baby into a toad!"
Toad's suits are painfully gaudy, but Lucas felt that they were integral to the character. "I have the shape of Toad, with my own little belly, and then another added on by the costume department." He has been bald since the age of six. "It's not great in terms of personal vanity, but then, I have played a watermelon with Vic and Bob, and been in a romper suit in Shooting Stars, so after that, you don't have an ego or vanity. Costume is sometimes cumbersome, but always worth it."
Lucas says that what he most enjoyed about Hall's script for The Wind in the Willows was that it stuck very closely to Grahame's book. "It's a very rich screenplay, but it remains a pretty faithful adaptation. It's not trying to be crassly different. It's not set in Iraq." Pause. "It's set in Iran."
Lucas is always ready with a quip, as funny off-stage as on, but his sense of humour has been somewhat tested recently: Lucas and David Walliams, his Little Britain co-star, have fallen victim to "tall-poppy syndrome". Lucas says: "I know that sometimes the British feel uncomfortable with other people's success. They say, 'OK, we've given you praise. Now you either need to go away or we'll start to criticise you.' But if that's the price you pay for doing your dream job, it's a small one. It's not something you can control, and there's no one famous that it hasn't happened to.
"Recently, the papers ran a story that there were tensions between David and me. That just isn't true - he's my closest friend. We get along better than ever. We've been bonded by what we've experienced together. It's not the first such story, and it won't be the last. I'm afraid these stories are a by-product of the success of Little Britain, but David and I just chuckle about them.
"When people occasionally say they don't like Little Britain, that is nothing compared to the fact that 9.5 million tuned in to the first episode of the last series. The negatives are minute compared with the privilege of being allowed to do our own thing on TV. If the worst that happens is that I wake up and see a picture of myself and a headline saying, 'He wasn't very funny last night', then I've got nothing to complain about."
Lucas and Walliams were not overnight hits; they toiled away for several years on the comedy circuit before Little Britain took off in 2003. "Success came to us at an age where we could enjoy it," Lucas reflects. "We went through a lot of hard times, so we appreciate success all the more now." The Little Britain live show - seen by almost a million people in this country in the past 14 months - is now heading for Australia. After that, Lucas and Walliams will be making a version of the sketch show for a US network. Little Britain, the show with the parochial title, is becoming a global phenomenon. "Even when I was in Romania [where The Wind in the Willows was filmed]," Lucas recalls, "people would come up to me and say how much they loved it."
Lucas was recently granted the ultimate celebrity accolade: an appearance on Desert Island Discs. "I was very humbled to be asked," he says. "But it was really difficult to choose just eight records. For weeks, I was flapping around, thinking, 'Oh my God, I've got no Abba!'.
"But I'm sure Benny and Bjorn will get over it. And, in the end, doing the programme was no great hardship. After all," he adds with a self-mocking laugh, "what actor doesn't enjoy talking about himself for hours on end?"
'The Wind in the Willows' is on BBC1 tonight, at 6.20pmReuse content