A biography due to be published by Faber and Faber in November will reveal that Pinter's play Betrayal was influenced by his relationship with Miss Bakewell, which lasted from 1962 to 1969. It had been assumed that the 1978 play was based on a later liaison, starting in 1975, with the biographer, Lady Antonia Fraser, daughter of Lord Longford and then the wife of a Tory MP. Pinter left Miss Merchant for her and she became his second wife in 1980.
But in Michael Billington's forthcoming biography The Life and Work of Harold Pinter, Miss Bakewell reveals: "Betrayal is about my relationship with Harold and it's all true."
"The affair described in the play was so intense," the Everyman presenter says, "that one can't ever forget how fraught it was and how riddled with moral underpinning. As we lived through the events, there really was a moral imperative to do the right thing. It was a serious matter and I think it took Harold a long time to decide to come to terms with it by writing about it."
The affair began when Pinter had already found fame as the author of The Birthday Party and The Caretaker. Miss Bakewell had begun her television career and was married to Michael Bakewell, a radio and TV drama producer. By the time it ended, she was one of television's most famous faces: as presenter of Late Night Line-Up, she combined intelligence with an understated but undeniable sexual allure, which led to her celebrated epithet, "the thinking man's crumpet".
The biography discloses that Michael Bakewell learned about the affair two years after it started but said nothing.
Perversely, this silence was seen by Pinter as itself a form of treachery. Michael Bakewell backed Pinter at the BBC, helping to get his plays on the air. "Obviously our friendship had ended by the writing of Betrayal," Mr Bakewell told Billington. "I remember vividly Harold's indignation at the fact that I had known for a long time about the affair without saying anything. I think he personally felt betrayed."
Betrayal depicts a seven-year affair between Jerry, a literary agent, and Emma, who is the wife of his best friend, Robert, a publisher (who himself has recurrent affairs). Emma survives the deceit with aplomb. The two men, symbols of parasitic, middle-class, middle-aged business people, are spiritually devastated by it.
Throughout the play (later made into a TV film), a single moment at a party when Jerry throws up Emma's baby daughter Charlotte into the air and catches her, is used as a symbol of pure happiness, lost for ever. This moment, according to Joan Bakewell, was, like many parts of the play, based on incidents during her affair with Pinter. In another important scene, Robert picks up a letter at the American Express office in Venice which is addressed to his wife in Jerry's handwriting. It is the moment when he realises the betrayal of his friendship. According to Ms Bakewell, one of Pinter's letters to her was found by her husband in the same way.