Michael Fassbender and Keira Knightley have joked about their spanking scenes in their film 'A Dangerous Method'

During the pair's joint appearance on the latest episode of 'The Graham Norton Show' on the BBC, Keira told the audience about the movie: "Basically it was about spanking. Michael had to spank me."

Michael chipped in: "I was the spanker. You were the spankee."

And opening up about the efforts that went into making the spanking scenes realistic but not too sore, Michael went on: "To get the right level of spank, it can't hurt too much, I suppose."

Referring to Britain's thick public phone book, he added: "There was a Yellow Pages between your bum and the paddle!"

Keira added about the scenes: "I bought Michael and three other cast members their very own spanking paddles.

"I had to go into a sex shop and say, 'Hello, can I have three spanking paddles, please?'"

Michael was on the Graham Norton show to promote about his new TV series 'The Agency', which sees him play an undercover CIA agent.

He also revealed how he met real-life spies in his research for the role, adding: "I think a lot of spies are just dying to tell you they are a spy. A lot of them watch these sorts of series and are very interested in them."

'The Agency' is based on the French show 'The Bureau' and was produced by George Clooney and Grant Heslov through their company Smokehouse Pictures.

Along with Michael, the show also stars Richard Gere, Jodie Turner-Smith, Hugh Bonneville and David Harewood.