The enduring mystery of why EM Forster failed to write any novels beyond his mid-forties has been solved thanks to a secret cache of papers in which he confided his sexual desires.

The author did not write any novels between the publication in 1924 of A Passage To India, one of his best known works, and his death in 1970.

Now Forster’s papers, including his “sex diary”, which had been locked away at his former lodgings at Cambridge University, indicate his creative drive was curbed after he lost his virginity to a wounded soldier on an Egyptian beach when he was 38 and met his long-term lover — a married policeman — several years later.

The author felt he could not continue to write about the heterosexual, English middle-class themes with which he had made his name.

“I should have been a more famous writer if I had written or rather published more, but sex prevented the latter,” Forster wrote.

The author, who was known to his friends as Morgan, his middle name, had written A Room with a View, Howard’s End and Where Angels Fear to Tread by the time he was 30. But his precocious talent was overshadowed by his repressed homosexuality.

“He never had sex until he was 38, although he never had doubts — even from a very young age — that he was gay,” said Wendy Moffat, associate professor of English at Dickinson College, Pennsylvania.

Moffat has gained access to Forster’s previously unseen papers for a new biography. The documents include the “sex diary” at King’s College, Cambridge, where the author kept a room from 1946 until his death.

After having sex for the first time while working with the Red Cross in Egypt towards the end of the first world war, Forster wrote in his diary about “losing R”, or respectability.

Yet he had written his only gay novel, Maurice, about two young men at Cambridge and a gamekeeper, some years earlier in the early 1910s.

The book was not published until 18 months after Forster’s death, however.

“Writing such a novel was a testament to Morgan’s extraordinary imagination,” said Moffat, whose biography will be published by Bloomsbury on June 14.

The diaries reveal that nearly all his lovers had working-class backgrounds and included bus drivers and sailors.

“I want to love a strong young man of the lower classes and be loved by him and even hurt by him,” he wrote.

Two of his most significant relationships were with police officers — an irony because homosexuality was illegal at the time. According to Moffat, one of these, Bob Buckingham, became “the love of his life”.

The relationship with Buckingham began in 1930 and continued, despite a few other flings, until Forster’s death in 1970. He did not write a single novel during this time.

“The marriage plot fiction had become a masquerade to him,” said Moffat. “Yet he could not bring himself to publish Maurice, which would have outed him.”

Alan Hollinghurst, the gay prize-winning author, said: “It is certainly true for quite a few writers and certainly for Forster that suppression [of sexuality] was a strong creative force. And yes, the happiness he found from a relationship took away the urgency of his writing.”

Buckingham was married throughout most of the affair, with Forster getting on well with his wife, May, and the couple’s son, Robin.

Indeed Forster, whose books have been made into Oscar-winning films, bought the Buckinghams a house and financially provided for them during his lifetime and in his will. The author was deeply upset when Robin died at the age of 29.

Forster died in the Buckinghams’ home after suffering a stroke at Cambridge. He was taken to their new residence in Coventry knowing he had only days to live.

His earliest diary entries about sex referred to masturbation as a youth. He continued penning his thoughts well into old age, however.

A poignant entry states: “Now I am 85 how annoyed I am with society for wasting my time by making homosexuality criminal. The subterfuges and the self-consciousnesses that might have been avoided.”

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