Sitting in his warmly furnished living room in Regent’s Park, in central London, Nicholas Mosley evokes an air of elegant bohemianism. A celebrated Booker-nominated novelist, winner of the 1990 Whitbread prize for his richly experimental Hopeful Monsters, he is also a skilled memoirist and has worked as a scriptwriter for the film directors Joseph Losey and John Frankenheimer. Now 86, he has just published a new novel and another memoir.

Educated at Eton and Oxford University, sustained by a private income, a baronetcy inherited in middle age, Nicholas has an air of quiet authority and detachment typical of the well-cushioned upper class but an effervescence all of his own. Almost as soon as I sit down, he says, “It’s very fashionable now to say one has had a terrible life. But I have had a rather good one.”

This lightness of spirit is all the more remarkable when you consider his background. For Nicholas, the eldest son of Sir Oswald Mosley, founder of the British Union of Fascists and half brother of formula one boss Max Mosley, is not just a member of one of Britain’s most renowned and controversial public families, he is that most dangerous of creatures – a writer in, and about, the family.

The Mosleys have been back in the headlines of late. Images of Oswald, strutting down London streets in his black shirt, have resurfaced following the election of two BNP MEPs in June. Max Mosley shot to unwelcome prominence last year after being caught engaging in S&M sex games, and subsequently taking on the News of World over intrusion into his privacy. Last week, he agreed not to stand for re-election as president of motor racing’s governing body. This all followed the tragic death of his eldest son, Alexander, 39, in May from an accidental drug overdose.

Of all Oswald Mosley’s children, Nicholas most clearly rejected his father’s rightwing politics while at the same time acknowledging mixed feelings about those close to him. Yet, in the end, Oswald Mosley chose Nicholas to be his official biographer. The resulting two volumes, Rules of the Game and Beyond the Pale, both published in the 80s, offer a candid account of Mosley’s private and public life, which went down well with reviewers.

But the wider Mosley family, including Max, were incandescent. After initially praising the book, privately, Oswald’s second wife, and Nicholas’s stepmother, Diana, told the press it was “the degraded work of a very little man … It’s all very well having an oedipal complex at 19, a second-rate son hating a brilliant father, but it’s rather odd at 60. Nicholas wants to get his own back on his father for having had more fun than he’s had.”

Max, meanwhile, circulated a dossier of the most damaging reviews, suggesting, says Nicholas now, that “I had deliberately set out to destroy our father. He also said, in effect, that I would die dishonoured, (that) no one would be interested in my dismal love affairs or unread novels.” He has wondered since if all this passionate resentment was “a mark of the family’s own reluctance to look at any truth about my father?”

The half brothers did not speak for decades, and it is only in recent months that there has been a rapprochement. Nicholas says, “When all that sex business happened, I felt so sympathetic to him, I thought he behaved so bravely [in respect of the court case]. I wanted to write to him and say, ‘I haven’t heard from you for 30 years but good luck’.” He did not, he says, because he was worried that someone might intercept and misinterpret the letter.

“But I did write to Max and Jean when Alexander died. To say how terribly sorry I was. Verity [Nicholas’s wife] and I went to Alexander’s funeral.

“Then Max pretty well flew straight off to Paris for hours of tough formula one negotiations,” he adds, with a noticeable trace of brotherly pride,

Nicholas treats other family ruptures with the same thoughtful levity. He also fell out with his brother Michael for 20 years, over something neither brother can now recall. They are back in touch and have met up. “It seemed crazy not to,” he says, adding, with laughter, “of course we got on terribly well”.

Nicholas’s childhood was, from the beginning, marked by distance from family. The main figure in Nicholas’s young life was his “darling nanny”. His mother died when he was nine. His father was a rather jokey figure, always hamming it up, fond of teasing wordplay. “But he did not want to involve us in his politics, even when he was in the Labour party [during the 20s]. And we never saw him in a black shirt, ever.”

His father became embroiled in fascism when Nicholas was still in his teens. How did he deal with Oswald’s infamy? He answers without hesitation: “I was saved from being a fascist by going to Eton. And I was saved from being an old Etonian by having a fascist father. “Eton was full of people from the wrong side, as it were. It didn’t worry them. When my father was imprisoned for his far-right political activities, people might pass me and say, ‘Hard luck about your father’ and that would be it.”

He says the same about the army, in which he saw distinguished war service: “It didn’t matter a damn if he was in prison, defying the logic of the war. I was in the army. And I was an officer.”

Nicholas has fond memories of “freewheeling conversations about politics, philosophy and the meaning of life” with his father, particularly during the war period, when Oswald was interned at Holloway prison.

But father and son clashed when Oswald returned to active politics after the war, standing for election, on an anti-immigrant ticket in Notting Hill, west London in the late 50s when he started “acting like an insecure racist with a virulent chip on his shoulder”.

Nicholas, then “at the height of his Christian enthusiasm”, went to his father’s offices to tackle him, on both his politics and a family matter. “I was full of passion but I didn’t know if I was trying to save his soul or my own. When eventually I was let into his office I said to him, ‘You are being wicked. You’re being insane. Just as you were in the 1930s.'”

Nicholas also told Oswald that he was a lousy and vindictive father. “I had expected a thunderbolt to descend, but my father just said quietly, ‘I will never speak to you again.'” They did, but not for many years.

Oswald was serially unfaithful to Nicholas’s mother. “He had no guilt or perhaps he simply couldn’t feel it. His two passions were politics and the pursuit of women.” And Nicholas did get “a little talk” from his father when he was a young man, implying that “infidelity was OK as long as it was only with married women. It was all very Jane Austen.” Nicholas laughs now, “because really it was all about money. You couldn’t ruin an unmarried girl’s chances by sleeping with her.”

But he adds, more thoughtfully, “while my father treated [his affairs] like a game, I took it all terribly seriously.” This seriousness is evident in his own recent memoir, an exploration of his creative, religious and emotional life after leaving the army. He begins to see that he is repeating a pattern in his father’s life, making both his first and second wife unhappy with his twin obsessions: work and other women.

It is only in his second marriage, to Verity, a woman 20 years younger, that Nicholas finds some kind of durable contentment, although even here he is abrasively honest about the marriage’s conflicts, including one isolated incidence of violence on his part.

Verity is equally straightforward. When I arrive to do the interview, she says briskly: “Well I will leave you two alone. I am likely to quarrel with everything Nick has to say to you.” Yet Nicholas looks up at her with something approaching adoration.

Nicholas has five children, but, understandably perhaps, writes less of his own life as a father. It is one thing to be scrupulously truthful about an already infamous public parent, quite another to drag one’s children into the story.

At the close of our interview, he tells me how moved he is by how apparently “faithful and good” the marriages of his own children are, and how he admires them enormously.”I don’t think I was a good father. I did have all these infidelities. But I like to think I was always honest and open. Children become aware of family troubles anyway. But they can learn: either these can become crippling, or not all that important in time, if confronted.”

This piece was first published in the Guardian in 2009.