The writer talks to Bridget Galton about the trouble in sorting fact from myth when your subject is an ex-spy raised in a house of deceit.

Former spy and professional storyteller John Le Carre was never going to be a straightforward subject for biography.

Add in a conman father who lied for a living, and untangling the truth proved tricky for Adam Sisman, who would meet the author – aka David Cornwell – over lunches at The Wells or in Hampstead High Street to sort myth from false memory.

“Part of the problem is he has told different stories at different times and no longer knows what’s true,” says Sisman.

“He’s been a bestseller for 50 years, re-telling his past in so many interviews and re-interpreting his life in his fiction. Many things he told me didn’t add up.

“He might have tried to steer me away from uncomfortable truths but I don’t think he deliberately tried to deceive me.”

Sisman foregrounds these biographical problems in John Le Carre: The Biography (Bloomsbury £25) by often offering both versions of a story.

“Once over lunch in Hampstead, David was explaining how he came to teach at Eton.

“I said: ‘I am sorry David, you have got that wrong, that doesn’t correspond with the records’. His mouth dropped open in surprise. He doesn’t like being depicted as less than straightforward; he once burst out: ‘Why do you always believe other people rather than me?’ I often did believe him. I have tried to tell the truth as it appears to me but make it clear it’s not easy to be sure.”

The author of A Perfect Spy and The Spy Who Came In From the Cold explained from the off it was hard for him to speak freely about his work for the intelligence services – or his messy personal life.

Sisman says you don’t have to be a psychiatrist to trace Cornwell’s chronic infidelity and future career to his miserable childhood with fraudster Ronnie and mother Olive, who left when he was five.

“He grew up in a house full of mysteries and disappearances. Brought up in a world of deceit where you had to fabricate to survive. Having such a domineering father meant he had to develop a secret life. He started spying, going through his coat pockets to find out what was going on – his father didn’t admit until he was an adult that he had served a term in prison. His mother left late at night without saying goodbye, no-one explained where she had gone. It was a very searing experience. It’s heartbreaking to think of a little boy saving his sixpences to get on a bus to go and find her.”

As a boy Cornwell told his peers his father was a spy. “He was of the generation during the war when what your dad did was terribly crucial. Ronnie was that most despised person, a profiteer, rather than away fighting. David fantasised and made up stories that his father was a secret agent.”

By the age of 17 he had been recruited by MI5 to spy on student groups in Bern where he had run away from his hated boarding school. Later at Oxford he spied on left wing fellow students.

“He is the perfect spy, a chameleon, extraordinarily seductive. Like everyone he meets I found myself falling under his spell,” says Sisman.

“He’s extremely charming, a brilliant linguist, a wonderfully entertaining raconteur and mimic – he does a good Mrs Thatcher.”

As “an old fashioned patriot” Cornwell was willing to do morally questionable tasks for his masters.

“I spoke to a Jewish schoolboy he befriended who thought he was a close friend of David’s and found out 40 years later he was reporting back to M15. He was very upset. The moral dilemma that runs through Le Carre’s work, personified by George Smiley, is whether the cause is worth the human suffering.

“He worries a lot about whether he has a moral centre. His big fear is that he is like Ronnie, who was also an extraordinarily charming man but a sociopath, with no boundaries. He robbed old ladies – his own mother – of their life savings and fumbled his own children when he came home late at night. He had no scruples. David regarded him with a mix of horror and love.”

And although he looked after her in old age, he still hasn’t forgiven his mother for leaving.

“He’s seething with anger. It’s affected his feeling about women. As Magnus Pym says, ‘they are untrustworthy people who abandon you’.”

Sisman says Cornwell’s pain is the reservoir upon which he draws for his often autobiographically-informed novels that began in 1962 and frequently hinge upon personal betrayal.

“He says his life has been really wretched and the only thing that he looks back on with satisfaction are the books.

“For most of us our sense of identity is bound up with being loved by our parents but he was totally rejected. You can argue an unhappy childhood gives a novelist the grit to write. Without it he may have been a happier person but never have become John Le Carre.”

The 84-year-old divides his time between homes in Hampstead and Cornwall, where he’s often seen striding along the cliffs acting out his character’s lines.

“People there are used to him muttering to himself and know not to bother him. He doesn’t like London or literary society, he’s not very clubbable as they used to say.

“He’s slowing down a bit but still writing, still driving himself on. The question is why?”

Although their relationship became strained at times, Sisman remains an admirer of Cornwell’s work.

“He’s dismissed as a genre writer but he transcends genre and will still be read 50 years from now as a quintessential novelist of the Cold War and for his extraordinary observation of men in strange institutions. Our relationship is always very cordial. He says its continuation is an achievement in itself. I hope I haven’t succumbed to the spell of the wizard and preserved that splinter of ice in my heart that every writer needs.”

Adam Sisman speaks about his book at Bloomsbury Academy on November 17. Visit bloomsbury.com/Bloomsburyinstitute