Benedict Cumberbatch kicks off London Film Festival

Hundreds of screaming fans welcomed Benedict Cumberbatch on the red carpet at the gala opening of this year's BFI London Film Festival.

The Sherlock star plays computer pioneer Alan Turing in wartime drama The Imitation Game.

Speaking at the film's European premiere in a wet and windy Leicester Square, Cumberbatch described Turing as "an extraordinary man".

His performance is already being tipped as an Oscar contender.

"To be asked to play such a phenomenal human being - a true English hero - is a great honour and comes with a great responsibility," Cumberbatch said.

He added that he had known "embarrassingly little" about Turing before he made the film.

"That's the tragedy of this man's extraordinary life - his achievements and his heroism and his criminal prosecution are not well known. He should be on the front cover of text books."

Co-star Keira Knightley and other members of the cast - including Charles Dance and Mark Strong - also braved the rain on the opening night of the festival. Knightley plays Turing's close friend and fellow-code breaker, Joan Clarke.

London Film Festival director Clare Stewart described The Imitation Game as "a remarkable British film with great British talent in front of the camera".

She told the BBC: "There have been people waiting for the red carpet since 4am - I'm thrilled that Benedict Cumberbatch and Keira Knightley decided not to take a rain check."

The Imitation Game stars Benedict Cumberbatch as computer pioneer and mathematician Alan Turing

The Imitation Game is largely set at Bletchley Park, Buckinghamshire, where Turing and his team attempted to decipher German messages to help end World War Two.

Turing killed himself in 1954, two years after being prosecuted for gross indecency after he fell foul of anti-gay laws at the time.

Turing received a posthumous royal pardon in December 2013, with Justice Minister Chris Grayling saying he undoubtedly shortened the conflict and saved thousands of lives.

Earlier on Wednesday, Cumberbatch said he understood why some people drew comparisons between Turing and his TV role as problem-solving genius, Sherlock Holmes.

"I didn't read the script and go 'this is Sherlock in tweed'," he said. "I liked how uncompromising he was and I suppose that's a strong trait in strong characters."

The film's Norwegian director, Morten Tyldum, described Turing as "an unsung hero who achieved so much... he was ahead of his time and outside of his time and was carrying all these secrets".

Some 248 feature films will be presented over the 12-day film festival, which runs from 8-19 October.

Among the stars expected on the red carpet are Brad Pitt, Shia LaBeouf, Timothy Spall, Andrea Riseborough, Sophie Okonedo, Noomi Rapace, Viggo Mortensen, Steve Carell, Sienna Miller, Reese Witherspoon, Dominic West and Emily Watson.

Another World War Two drama, Fury - starring Brad Pitt - will close the festival on 19 October.

Pitt will attend the premiere with director David Ayer, who said it was "a true pleasure to be returning to England, where we shot the film". Many of the action scenes were filmed in Oxfordshire.

Set in 1945, Fury tells of an army sergeant in command of a tank crew for a mission behind enemy lines.

Commenting on the WW2-themed films that open and close the festival, Stewart said: "Our filmmakers are returning to themes about war - including our centrepiece gala Testament of Youth. Our times make us return to these stories of conflict to try and understand the human condition a little better."

Other gala screenings at the festival include wrestling drama Foxcatcher, starring Steve Carell; and Wild, with Reese Witherspoon as a young woman on a gruelling 1,100 mile hike. The film's screenplay is written by Nick Hornby.