James Corden: Do I sing? No Chance!

James Corden has confessed all his vocals are dubbed in new movie One Chance about Britain's Got Talent winner Paul Potts.

The Gavin And Stacey star was at the Toronto Film Festival for the world premiere of the film, where he was joined by Taylor Swift, who composed a song for the movie, Alexandra Roach, who plays his on-screen wife, and Paul Potts himself.

Despite being able to sing himself - James is about to begin filming Hollywood musical Into The Woods - the comedian admits his opera isn't up to scratch - so Paul's own voice was dubbed over him into the film.

James revealed: "It was very, very straightforward, I would pretend to be singing opera, and then Paul would go into the studio and loop to my mouth. I hope I haven't given it away too much, but that's basically what happened."

The actor also admitted he found it less pressure to play Paul because the film ends at the minute he walks into his first Britain's Got Talent audition, when the nation all came to know and love him.

Taylor revealed she signed up to the project because she was so moved by the story of the mobile phone shop worker from Wales who shocked everyone with his amazing voice.

She said: "It's amazing to be a part of this project. It's a movie that really moved me in a way that I haven't been moved in a long time, and to have just a small part in telling the story... I wrote the end-credit song so it's the last thing you see of the story and I'm really, really honoured."

The Iron Lady star Alexandra recalled watching Paul Potts win Britain's Got Talent back in 2007.

She revealed: "I was in hospital at the time and I remember me and three old ladies gathered around the communal television in our ward, and we watched him sing.

"And because he was from Swansea and I was in a South Wales hospital then we were all crying and weeping and really rooting for him. And it's so bizarre now to think that I'm sharing a red carpet with him and I'm playing his wife! It's mad!"