William Cash is a seasoned journalist, having worked for ten years in Los Angeles for The Times newspaper, covering the OJ Simpson trial, and blagging his way into interviews with movie stars and high society. But the world of literary biography has him stumped. He was so annoyed with reviews of his book on the writer Graham Greene that he set up a website to counter the criticism.

“Welcome to the bitchy world of literary biography,” says Mr Cash when I ask him about it. “It was entirely predictable.”

A Roman Catholic, son of the controversial Tory MP Bill Cash, he believes Greene’s “moral universe” in which “the decisions that people make have consequences” has plenty to tell us today.

The trouble started when he was given access by Greene’s literary executors to letters written by the author of The End of the Affair to his mistress Catherine Walston. Greene famously abandoned his wife Vivien and children just after the Second World War. The family lived first in Beaumont Street, Oxford, and later at Grove House in Iffley, while Greene moved in with a string of mistresses.

He never divorced Vivien, who stayed at Iffley until she died in 2003 at the age of 98.

Cash will talk at the Oxford Literary Festival on Saturday about the part Oxford played in Greene’s relationship with Walston.

“People think that it happened during the war, in the Blitz in London, but The End of the Affair was written in the late 1940s, while Greene was in Oxford.”

Cash does not subscribe to the theory that The End of the Affair is the disguised story of his relationship with Walston. “Greene was far more complex a writer than that, and a lot of it was from his imagination, but obviously it was connected to Catherine Walston.

“In 1948, Greene was living in Beaumont Street and commuting to London, where he was living, unbeknownst to Vivien, with his mistress Dorothy Glover.” He believes the relationship with Catherine was more intense than any other in Greene’s life, and that it played an important part in his writing.

Cash’s book The Third Woman (Abacus, £8.99) came out in 2000, at the time of a new film of The End of the Affair. It includes a lengthy interview with Vivien Greene at Grove House only a few years before her death. The author believes she was relieved at the chance to talk about the affair, which was still painful to her. “She was not bitter at all.”

Cash says the access to the archive, granted by Greene’s son Francis, led him into a “hornets’ nest” of problems. “I was being attacked on both sides. First I had issues with Norman Sherry, Greene’s authorised biographer, and his lawyers.

“On the other side I had Oliver Walston, Catherine’s son.”

He has now put the bad reviews to one side, including one in The Times by Oxford writer Humphrey Carpenter, and emphasises the good ones by Selina Hastings and AN Wilson.

But asked about his future writing plans, he says: “I would never do another literary biography. Firstly, there is zero money in it. Secondly I always wanted to write for the theatre, and I had a play at the Edinburgh Festival, The Green Room, about the Oxford philosopher Freddie Ayer.

“Third, there was the hornets’ nest that I stirred up when I tried to get access to the archives. I would never do that again.”

He started a publishing company, Spears, which he describes as a “financial version of the New Yorker” and which he has now sold, so has more time for his latest project — providing a retreat for established writers at his estate, Upton Cresset Hall, in Shropshire.

His foundation will award fellowships four times a year, which he says might be ideal for Oxford academics who want to get away to a peaceful place to write a book.

He will share his slot at the Oxford Literary Festival on Saturday with Lara Feigel, an academic who is writing a book about Greene and other post-war authors.