A new biography claims British writer SIR John Mortimer cheated on his first wife on numerous occasions and enjoys sado-masochism.

Author GRAHAM LORD lifts the lid on what he claims is the 82-year-old creator of TV show RUMPOLE OF THE OLD BAILEY's secret life in new book JOHN MORTIMER: THE DEVIL'S ADVOCATE.

Lord writes of Mortimer's 80th birthday party thrown by author KATHY LETTE, "(She) risked over-exciting him by taking him to a restaurant in Covent Garden, School Dinners, where the waitresses were dressed in skimpy schoolgirl tunics.

"To stimulate him beyond endurance she took him also to another 'erotic' London venue, Club RUB, which should be 'huge fun', she twittered.

"'It's all quite naughty and they whip you with lettuce and things'. 'Lettuce? What no hairbrush?'"

Mortimer, father of actress Emily Mortimer, says of the book, "Oh God. But what can I do? I can't stop it. It's a rather unpleasant book.

"Graham Lord told me he was going to write the book, and then told the publishers that it was authorised. So we didn't want people to talk to him. It's very upsetting."