The secret lover Rupert Brooke romped naked with through Grantchester meadows was not a bohemian wild child as she has been portrayed, her defenders claim.

Phyllis Gardner, the young artist whose tempestuous affair with the patriot poet Churchill idolised as "one of England's noblest sons" only came to light when her 90-page memoirs were unearthed in the British Library, was an innocent who doggedly clung to her virginity.

Brooke became so frustrated with her defence of her virtue that during an erotic encounter he pretended to strangle her, an experience she later confessed she had quite enjoyed.

The discovery of the papers, locked away for 50 years at the request of Gardner's sister Delphis, confirmed the growing impression that Brooke was far from the noble martyr of myth but could be a cruel and manipulative cad, whose charisma and beauty allowed him to get away with murder.

With poems such as the The Soldier, Brooke became the laureate of the generation lost in the first world war, his sanctity confirmed by his early death on the way to Gallipoli. Biographies and memoirs by his friends Eddie Marsh and Geoffrey Keynes cultivated this image of a pure and ethereal young man who sacrificed himself for his country.

What they failed to mention was that Brooke was a lothario who at one stage, according to his most recent biographer, Nigel Jones, kept four relationships on the go at one time, was bisexual in his youth, and also managed to conduct affairs with two sisters simultaneously, without either of them knowing the full story.

Nor was there any mention of Phyllis, although Marsh met the artist several times and allowed Brooke to use his London flat as their love nest.

Lorna Beckett, an artist herself, became convinced five years ago that there had been a love affair when she found a copy of a woodcut showing Gardner grieving over Brooke's grave on the Greek island of Skyros. Gardner fell for Brooke after she spotted him on November 11 1911, when he sat opposite her on the Cambridge train and she started to sketch him.

The spark of attraction was mutual but it did not combust until he invited her to his home, the Old Vicarage in Grantchester.

After they stripped to wade across the Cam, she threw his boots into the river and he chased her, bringing her down in the meadow. Brooke's mood suddenly turned. He said: "Supposing I were to kill you?" He then gripped her around the neck. "I was in a sort of heaven although once he made me choke," she wrote later.

Brooke left for Berlin soon afterwards, where he wrote his most sexually charged poem for her, Beauty and Beauty.

But Beckett believes the couple never slept together. She said Brooke had wanted them to have sex and it was his pressuring of her which broke up the relationship.

"He had no intention of marrying her and that is what she most wanted. She wanted to save herself. She sacrificed the love of her life for her principles. That is why I feel so sorry now for Phyllis that she is being portrayed as some kind of loose woman."

The news of Brooke's death from septicaemia in 1915 seemed to unhinge Gardner. Eventually she dedicated her life to breeding Irish wolfhounds and working as an illustrator.

Nigel Jones, whose new biography of Brooke, Life, Death and Myth, revealed that the poet had gone on to father and disown a child by a Tahitian woman, said Gardner - like many of Brooke's lovers - was prepared to overlook his vain, neurotic side.

"He overwhelmed people. You just have to look at his letters to see that. He is probably the greatest literary letter writer since Byron."