Nick Park doesn't strike you as a man who would say "no" to an Hollywood outfit as powerful as Disney. His manner is more frightened mouse than roaring lion. But when it comes to plasticine, he knows what he wants - and the people at Disney made him an offer he could refuse.

He appears to hanker after neither fame nor fortune although, as the creator of Wallace and Gromit and being worth an estimated £12m, you could say he has achieved both already.

At heart, he's a man at his happiest fiddling about with pieces of plasticine rather than getting out there in public promoting himself. "I would rather be behind the camera than in front of it," he admits nervously.

Even winning three Oscars (for best animated short each time) hasn't made those public appearances any easier. "It's very surreal," he says of attending the Academy Award ceremony. "One minute you have plasticine under your nails and the next minute you're squeezing through a door with Sharon Stone.

"You feel like a fish out of water. I just wish they would hold the ceremony on a day when you weren't so nervous. I didn't know if my legs would carry me on stage if I did win, whether I'd be able to get up there or faint or utter anything at all."

Park has been flushed out of hiding for the release of Chicken Run, the first full length feature film from Bristol-based Aardman studios. He and Peter Lord - who founded Aardman with Durham University graduate David Sproxton - directed this as part of a £150m four-picture deal with Steven Spielberg's Dreamworks studios. Ironically, it was Jeffrey Katzenberg who used to work at Disney and is now with Dreamworks who clinched the deal.

Lord says they rejected the Disney studio's offer partly because they didn't have any feature film ideas at the time and partly because "what they were suggesting wasn't attractive". The drawback was not so much the money as the terms of employment.

"They wanted to dominate us too much. Dreamworks came from a different place entirely. It's very much a partnership rather than working for them," he says.

"Disney were surprised we weren't only interested in the cash. They gave the impression they were the only game in town and you had to play by their rules. They were surprised when we didn't."

Park adds: "One thing Jeffrey learnt from us when he was at Disney is that we were more interested in creative freedom than anything. That's how Dreamworks approached us - as film-makers."

The result finds one of Hollywood's newest studios sending in a battery of chickens to take on the might of the Mickey Mouse studio. This weekend Chicken Run opens on 3,000 screens in the US. If audiences decide they feel like chicken tonight (and every night), it could hatch a whole egg-box of plasticine movies which budget-wise cost chickenfeed compared to other animated films.

Simply put, Chicken Run is The Great Escape with chickens: feathered inmates on a Yorkshire farm plot their freedom after learning of plans to turn them into the filling in chicken pies. As you'd expect from the Wallace And Gromit people, the action is peppered with sly humour and a darker edge than you'll find in Uncle Walt's animated features.

Aardman were willing to wait for the right conditions because they were only too aware of the problems of switching from short to full-length feature films.

"It's such a different game. Apart from practical considerations, that was what always held us back from doing a feature. How do you tell a story? How do you keep an audience hooked for 80 minutes?" says Park.

"That's partly why we didn't do a Wallace and Gromit film. Only one character speaks. So it would be hard, not that it would be impossible. We have a Wallace And Gromit feature in very early development - it's in my head. That's about four years off."

Park and Lord pitched the idea for Chicken Run out to lunch with Spielberg and Katzenberg. "Their eyes just lit up," recalls Park. "That's what gave us confidence in the idea. Steven Spielberg said, 'that's good, I have a chicken farm and The Great Escape is my favourite movie of all time'."

Park drew on his experiences working in a chicken-packing factory for the story but has no ambition to turn the world vegetarian. "Babe had that effect but it's not our intention. Our story is not really about chickens, it's about people. A human story in chicken costumes," he says.

For Aardman, making Chicken Run meant a big increase in workload and a deadline to meet as Dreamworks fixed the US opening date long before the film was completed. Many more animators were needed, 32 compared to the seven who worked on A Close Shave.

Lord and Park worked together for two years of pre-production and storyboarding but once shooting began they couldn't direct as one. "We had a big studio full of these sets and had to sprint around and direct ten to 15 sets each every day," says Lord.

"You want to do every frame. It's hard to let go and allow other people to do it," adds Park.

AbFab's Julia Sawalha, Jane Horrocks and Imelda Staunton are among the British actresses voicing the chickens. Outsider Rocky, "the lone free ranger", is voiced by Hollywood star Mel Gibson. And no, before you ask, employing an American wasn't a requirement of the deal.

"We went for a long time without casting anyone in that part," says Park. "It developed in such a way that Mel Gibson filled the shoes of Rocky perfectly. We'd seen him in Maverick and the character of Rocky was very similar. We took a line from Maverick and animated Rocky to that voice, and it worked perfectly."

They'd already met Gibson when they were in the States for the Oscars a few years ago. "As happens in Hollywood, people invite you out and we got this call from Mel Gibson to go out to his cigar club for lunch. We thought there was some deal about to be talked about but it turned out there was nothing at all. He just wanted to meet up with us. His kids were big fans of Wallace and Gromit. We all shook hands and went our separate ways.

"It was only about a year later we thought of him for Rocky. We thought why not go for someone we really want and he agreed, surprisingly."

l Chicken Run (U) opens on Friday (June 30)