By Arif Ansari Entertainment reporter, BBC News

Depp delighted fans by signing autographs despite the rain Depp's film singing

Actor Johnny Depp has met fans in London at the premiere of his new film Sweeney Todd: The Demon Barber of Fleet Street, based on the hit musical.

He was joined in Leicester Square by co-stars Helena Bonham Carter, Alan Rickman and Timothy Spall.

Depp, 44, plays legendary 19th Century serial killer Todd in a role which required him to sing.

"It was a challenge to see if I could do it. You've got to try something once and I gave it a shot," he said.

Depp spent almost an hour talking to fans, some of whom came from as far afield as Japan and Russia, and signing autographs.

Johnny Depp and Helena Bonham Carter star in Sweeney Todd

Director Tim Burton, who was also there, said he had wanted to make a film version of the story ever since he saw a stage production in London as a student.

He defended the film's bloody murder scenes, which have earned it an 18 rating in the UK.

"By having more blood, it actually made it a bit less graphic, because sometimes when you don't show stuff it has a tendency to be more real and disturbing," he said.

The story of Sweeney Todd, which dates back to the 1840s, is a vicious tale of murder and revenge, and is one of the first examples of a fictional serial killer.

It was turned into a play in 1973 and became a hit Stephen Sondheim musical six years later. Some of those revamped songs were being played out as the stars arrived in the rain on a very wet red carpet.

Unpleasant pies

Alan Rickman, who plays Todd's nemesis Judge Turpin, was also popular with the fans - and shared Depp's concerns with the singing.

"It was less singing and more careering from one note to another," he claimed.

Helena Bonham Carter loved the musical the moment she saw it

Burton said he had always planned to cast actors who could sing, rather than singers who could act.

It is the sixth time he has collaborated with Depp. Their previous films include Charlie and the Chocolate Factory, Edward Scissorhands and Sleepy Hollow.

Burton's partner, Helena Bonham Carter loved the gore. She plays Mrs Lovett, who recycles Todd's victims by serving up some particularly unpleasant pies.

"It's one of the best written roles for women ever. I loved it from the age of 13. I think I've always wanted to be Mrs Lovett," she said.

The film has been nominated for four Golden Globes in total, including best picture.