Revered as the puppeteer pulling the strings on Sesame Street and the man behind cult legend Yoda, Frank Oz is also a successful grown-up film-maker. He tells Donald Clarkeabout his latest movie, Death at a Funeral. Ask him anything, just don't ask him what Miss Piggy makes of his latest flick

Followers of Sesame Street, that delightful celebration of all that is generous in the American spirit, have long argued that clues to the relationship between Frank Oz and the late Jim Henson, the two men most associated with the creation of the Muppets, can be discerned from a glance at the goings on between squabbling co-habitees Bert and Ernie.

Ernie, originally voiced by Henson, is jolly, easygoing and open-minded. Bert, a creation of Oz, is brittle, humourless and anally retentive.

Previous interviews with Frank Oz, whose new comedy, Death at a Funeral, opens here today, do suggest that he - to use that most telling of euphemisms - does not suffer fools gladly. Many interviewers have founds themselves savagely slapped down after asking the wrong question about Oz creations such as Grover or Miss Piggy.

"I am still proud of Miss Piggy," he says. "Her character was neurotic and layered and I am proud of that. What I don't like - and haven't liked from the beginning of my career are the silly, trivial questions. I was asked last week: 'What would Miss Piggy think of Death at a Funeral?' How the f**k would I know? What sort of a f**king question is that?"

This outburst aside, Frank Oz turns out to be perfectly charming company. Now 63, he has a grey seriousness to him, but, once convinced that you are not going to ask him about Fozzie Bear's religious beliefs or Kermit the Frog's taste in music, he engages very civilly with the conversation.

Oz has been directing films starring fleshy humans for 20 years now and in that time has delivered hits such as Dirty Rotten Scoundrels and In & Out, as well as the odd flop such as The Stepford Wives and HouseSitter. Death at a Funeral, his 12th feature, falls somewhere between those two extremes. Following the fractious events at an English funeral, the picture, which stars Matthew MacFadyen, Peter Dinklage and Daisy Donovan, is an old-school farce in the style of the Whitehall Theatre or Georges Feydeau. People are forever exploding through doorways to discover things they would rather not see.

"Oh, that's right. It's totally farce," he agrees. "With that form you have this tricky first act where you have to tap dance round the introduction of all these characters. Then, in the second act, you have to establish a kind of desperation that makes their absurd actions in the third seem somehow believable."

It sounds as if he has thought this through. "Well, I am not sure I want comedy to be too heavily analysed. The moment somebody gets up on a dais and starts lecturing about comedy I run for the hills."

If Oz is to be believed, his career developed through a series of happy accidents that led him serendipitously from one triumph to the next. Frank's parents, European Jews who fled the Holocaust for England and then California, were puppeteers, but the young man always wanted to be a director. Still, he did a few puppet shows to keep his parents happy and, in his late teens, bumped into the imaginative force that was Jim Henson. Their creations for Sesame Street, which began in 1969 and still runs today, has illuminated a billion childhoods and diverted a billion more stoned students.

Was Oz aware while developing the show that he was involved in the creation of a timeless phenomenon? "Oh, no, I was just focusing on the work and making sure it was as good as possible. I put my heart and soul into it, but I was always aware it was work. I probably didn't realise how important it was until 30 years later. I never look at my old work. I don't linger over past stuff. What's the point of that?"

Still, he must occasionally catch sight of Sesame Street and long to get his fingers back on the puppets.

"Maybe I could be persuaded if there was an opportunity to make the Muppets more the way they were," he says. "They are now a little too soft, and I think Sesame Street has become just a little kids' show. When we were doing it, it was always geared towards both parents and kids. It was really quite hip. Now it's just for the kids."

The characters Oz created for Sesame Street and, later, The Muppet Show have an agreeable degree of depth to them. And he owns up that he devised intricate biographies for each of them. Come to think of it, he probably does know what Miss Piggy would think of Death at a Funeral.

"They were all created differently," he says. "There is no intellectual process to it. It is all to do with play and taking yourself down alleys. I don't know exactly where Miss Piggy came from, for example, but I do know exactly who she is."

After helping George Lucas create Yoda for the Star Wars films and directing the odd Muppet feature, Oz finally achieved his ambition and became a director of live-action features. It must have been a challenge dealing with humans alone.

"Oh, not at all," he exclaims. "Those Muppet films were the hardest things I have ever done. Honestly, shooting these recent films has been like a vacation to me after my time with the Muppets. You can't imagine how hard it was when a character can't even drink a cup of coffee on his own."

I suddenly imagine Bert, eyebrows angrily furrowed, scowling impatiently at a Muppet actor with Nescafé all over his, her (or its) shirt. There is certainly something in the comparison.

Frank Oz: a filmography

1982The Dark Crystal

1984The Muppets Take Manhattan

1986Little Shop of Horrors

1988Dirty Rotten Scoundrels

1991What About Bob?

1992HouseSitter

1995The Indian in the Cupboard

1997In & Out

1999Bowfinger

2001The Score

2004The Stepford Wives

2007Death at a Funeral