Rafe Spall, Asa Butterfield and Sally Hawkins have told how proud they are to premiere their film X+Y in their home town.

The film stars Butterfield as an autistic boy who finds a way to express himself through maths, Hawkins as his mother and Spall as his maths tutor who has multiple sclerosis.

It premiered at the BFI London Film Festival in Leicester Square tonight, with director Morgan Matthews also in attendance.

Spall said of the film: "It was a world I'd never seen represented before, that of mathematics being a beautiful thing. I'd never really thought of maths having beauty before, it hadn't been on my radar.

"You want to represent something such as autism properly, thoroughly and absolutely, without offending anyone who has that. Also my character has multiple sclerosis and you just want to do these things justice."

Of debuting the film at the festival, he added: "London's my city - I was brought up in London, I'm proud to be from London. It's the most glorious, civilised, wonderful city in the world, so to have a film at the festival is a real dream come true."

Butterfield agreed: "It means a lot, I was born and raised here, it's my home. To get to share the film with so many people here, it's great."

Hawkins added: "London Film Festival is so important and every year seems to be bigger and more starry.

"I'm really proud, we do it so well and we've got such great talent, so to celebrate it is wonderful. To be on my home turf is really special."

London Film Festival closes on October 19 when Brad Pitt will premiere his World War II film Fury.

X+Y is due to be released in cinemas on March 13 next year.