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We were stumped by crossword - Keira

Hollywood star Keira Knightley has told how she and fellow actors who play a team of gifted code-crackers spent five days trying to solve a quick crossword.

The 29-year-old said she and a five-strong group of colleagues - including Benedict Cumberbatch (inset right) - who portray encryption specialists in The Imitation Game were still unable to finish it.

She plays Joan Clarke, part of the team based at Bletchley Park in the Second World War who were tasked with unscrambling messages sent by the German forces using Enigma machines.

Knightley admitted that even when a maths expert came in to give the cast an explanation of the code-solving work, she struggled to grasp it.

"It was that feeling I haven't had since school being in maths, of not being able to concentrate at all."

Her character was among the recruits who had actually been brought on board after showing their ability by completing a cryptic crossword.

"One day we decided we should all really do the crossword. So we got the quick crossword and still didn't finish it," she said.