Halle Berry, Robin Williams and Jim Broadbent join Ewan in the cast of Robots. It's also a children's movie, set in a universe populated by mechanical beings. McGregor is the voice of an idealistic android, Rodney Copperbottom, a young inventor who dreams of making the world a better place.

Q: Did you choose to do these animations in order to have an easier time of it for a bit and be of-screen?

A: It was appealing to make an animation for my kids. I've got two girls and it was nice to do a film for them. Then, the stories were also very good. Thirdly, with Valiant it was a British animation and I wanted to be a part of it.

Q: Was part of the appeal that you could just roll out of bed and go to work?

A: There was that, too! It's actually easier to portray a character and tell their story when you're in costume, on location and being shot. When you're just doing the voice, it's very difficult.

Q: Ricky Gervais, who provides the voice for Bugsy in Valiant, said he felt utterly awkward but that you were a natural.

A: I just started before he did. I think I'd been in for a couple of hours and then Ricky arrived for us to do the scene together. You normally don't meet the other actors when you do animation at all. I'd already got in to the swing of things. I'm sure he was putting himself down.

Q: So have your kids seen the films? What did they think?

A: They've seen Robots and liked it a lot. My eldest is nine; my little one is three. I don't think my little one really had any idea. I kept going, "That's me, that's my voice," and she was all "Shut up!" My eldest, after 10 minutes, stopped even thinking about it and, I think, got sucked into the film.

Q: There's a lot of humour in Robots - did that jump out of the page when you first read the script?

A: Probably not as much as when you're watching the film. That's mainly because of Robin Williams, who ad libs like a dynamo. You just stand him in front of a microphone and he's off. I think most of his dialogue in the movie is stuff he came up with off the top of his head.

Q: Isn't that strange for you, when you come to see the final cut and loads of it is different?

A: Yeah, you just have to concentrate on your part. I would read all my scenes with the director, Chris, so I wasn't just doing lines at a time. It goes together seamlessly, somehow. It's kind of like magic - I don't really know how it works.

Q: The films you've done over the years have been so diverse, from Trainspotting to Moulin Rouge! to Star Wars, and now animation. Do you purposefully look for change?

A: It's not by accident that they are all different. I'm looking for stuff I haven't done before. I just keep a really open mind about it. Sometimes you can make a good movie from a mediocre script. I don't have a game plan, other than doing stuff that makes me happy.

Q: So what's next, then?

A: I'm going into theatre, doing Guys And Dolls. We open in June and I'm in that for the rest of the year.

Q: Does it daunt you, going back into live theatre after doing movies?

A: Yes, it's terrifying but it's so healthy for actors to be in theatre - it's really good for us. The process is very difficult. On stage, you have to tell the whole story and I think it's good for us to work together far more. There's something incredibly thrilling about that. It's brilliant and I miss it a lot. I miss the rehearsal room a lot too, so the idea of being in a rehearsal with a bunch of actors is fantastic. I can't wait, really.