Funnyman Robin Williams finds it hard to keep up with the demands of his fans, he tells Alison Jones.

It was Robbie Williams who sang “Let Me Entertain You”, but it is the fans of Robin Williams who seem to take it as a literal invitation.

Even a casual encounter can turn testy if he doesn’t break into a spontaneous gag-athon with a liberal sprinkling of impressions.

“A lady came up to me at an airport and said ‘Be zany!’,” he recalls. “It is like going up to Baryshnikov and going ‘Dance!’.”

“People want you to be on all the time and the first time you think you have to be, but it is really exhausting and can burn you out pretty quick.

“You have to say no. It is too much pressure. But sometimes if you don’t give somebody what they want they get like ‘He is being iffy’.”

Camera phones have only compounded the problem, he says, making everyone a potential paparazzi.

“They are like ‘Can I take a picture?’ and you go ‘Sure’. You stand there with their husband or their wife, and you go (he smiles politely) and they go ‘come on SMILE’.

“They want this,” he says, grinning maniacally. “That’s not a smile, that’s a seizure.

“I’m happy but they want something bigger than life, and I am like ‘this is me, I’m happy, this is real.”

He is not bemoaning his lot. Just the fact that some people seem to be able to divorce Robin the comic from Robin in real-life.

Fortunately they seem less inclined to see him “be” the serial killer from Insomnia or the creepily obsessed stalker of One Hour Photo.

These days he says he prefers to remain low-key, not just because he is a 60-year-old reformed coke addict and alcoholic who underwent heart surgery two years ago, but also because it is how he gathers new material.

“I am totally quiet out of the public view. The me at home is totally quiet. I ride my bike, hang out with the children, hang out with friends. When I am out it is me, just the observer.

“The only way to get new stuff is to watch and to learn, to listen. That is why either walking or riding around on a bike is so much better for me because you just see.

“I took the subways in New York about six years ago. I remember seeing this old wino going ‘What the hell’s Mork doing in the subway, Things are going badly, right?’.”

For all he protests against the expectation that he be “on” all the time, judging by the quips and eerily accurate impressions that typically pepper any interview with him, the compulsion to amuse clearly runs deep.

“I think the first time i did a voice, was as my grandmother. I used to do her for my mother...(affects a high pitched voice) ‘Sonny boy. I’m out here watching Motorcity wrestling’.

“My mother would go ‘that’s very funny, now stop’.”

His own children, he says, seem similarly unimpressed by the abilities that film studios pay millions for.

“I used to read stories to my daughter and I’d to do all the voices. Then my daughter, at one point, said ‘Just read the story’.

“I remember there was a famous scene with Sylvester (the cartoon cat) and his son where the kid is going ‘Oh fawther, mutht you embarrass me so” That’s me.

“I think ‘It paid for the house, don’t be ashamed’.”

Back in 1992 Robin set the bar in celebrity voice overs for cartoon characters after his show-stealing turn as the Genie in Aladdin.

He is back this week in Happy Feet Two, reprising his creations of Ramon, leader of The Amigos, a small group of Adele Penguins, who fancies himself a having a way with the ladies, and Lovelace, a Rockhopper penguin who has become a life and romantic guru for the Adeles.

The first Happy Feet won an Academy Award for its story of a tap-dancing Emperor penguin, Mumble, striving to be accepted by peers who value the ability to sing rather than dance.

That first film carried a heavy environmental message about over-fishing. In the sequel the penguins are endangered by shifting ice which leaves them trapped.

“The eco message in this is huge for me given that I live in San Francisco at sea level,” says Robin. “If the ocean rises even by inches, by a foot, I am screwed.

“Climate changes, it is real. You have to know from the storms the rain, the snow, the different things that are happening. If there is anything in the world we can do to diminish that then good luck.

“I ride my bike as often as possible.

“George Carlin used to say it best “the idea of save the planet – the planet is going to go on really fine without us. It is us that is in danger’. We are the one that could go bye bye.”

Talk turns to the fact that Robin is a newly-wed. He has already been married twice, and has three children. He wed graphic designer Susan Schneider, in October.

Clearly a man in love, he is surprisingly eager to (over)share the fact.

“It’s wonderful. She is incredible. It is exhausting,” he jokes unsubtly.

It seems that the third time could be the charm for Robin.

“It is different this time. She’s taller,” he quips.

“It is just easy and so comfortable. We are easy doing all different things, not just finishing each other’s sentences.

“She is an artist, a painter. The first time she was painting she came out of the room just covered in red. I said ‘Baby..! Oh, it’s paint’.

“But she looked like I do after I perform, a little frazzled and sweating. I went ‘Oh, so that is what is painting is for you’.

“She has that release. Her paintings are really powerful for me, not just because she is my wife, it is just that they are really vivid. I thought ‘It’s cool to know that you have that and I have this and that’s wonderful’.

“She is such a gift. I have been blessed.”