Britain’s own Kama Sutra of improbable sexual positions created by one of its greatest 20th-century artists has been brought out from under the bed.

Hundreds of explicit drawings created by Duncan Grant, a leading member of the Bloomsbury Group, are set to go on display after their rediscovery. They were thought to have been destroyed.

In the late 1950s Grant had given the trove of more than 400 drawings, mostly of all-male sexual encounters and created at a time when homosexuality was still illegal, to a friend, Edward Le Bas, in a folder marked: “These drawings are very private.”

After Le Bas’s death in 1966 it was thought the drawings had been destroyed because they were so explicit.

However, they ended up with the theater designer Norman Coates who said this week that he kept them under his bed and would occasionally “haul them out” to show to friends.

Bloomsbury Group painter Duncan Grant, who had an affair with the painter (and sister of Virginia Woolf) Vanessa Bell, as well as with economist John Maynard Keynes and writer Lytton Strachey, at age 90 in his studio at Charleston House, in East Sussex.

“Every single person was startled by them because they’re very graphic,” he told the BBC. “You couldn’t have sex in some of those positions, we all agreed. Although I think some went home and tried.”

Mr Coates has donated the drawings, valued at about $2.6 million, to Charleston, the former Sussex home of the Bloomsbury Group where, once it reopens, they will be put on public display.

Or at least some of the less explicit will.

“It’s quite a Kama Sutra of Duncan Grant’s sexual imagination,” Darren Clarke, the head of collections at Charleston, said. The 422 works on paper depicted “every conceivable act of couples”, he added.

“Every single person was startled by them because they’re very graphic. You couldn’t have sex in some of those positions, we all agreed. Although I think some went home and tried.”

Grant, who died in 1978 aged 93, had been a leading figure in the Bloomsbury Group, which remains one of the cultural world’s most cherished sets.

He had a child with Vanessa Bell, the sister of Virginia Woolf, but also counted the economist John Maynard Keynes and the historian Lytton Strachey among his many male lovers.

Mr Clarke said that the 422 drawings were created in the 1940s and 1950s when homosexuality was still illegal.

“There’s a strong theme in the work of interracial sex, of white and black males together,” he added. “Duncan Grant had black friends who were models, who were also lovers throughout his life.

“This is the inner life. This is his passion. This is what he was interested in.”

Mr Clarke said it had been easy to assume the drawings had been destroyed.

“That is the fate of a lot of queer history. Relatives have destroyed it to protect the reputations of the person who has died or the family as a whole,” he added.

Mr Coates said he had been increasingly conscious that the images he had kept under his bed needed to be seriously considered.

“They have been weighing heavily on my mind and I’ve been wondering who I might pass them on to, and I thought this could go on for centuries if we don’t kind of stop it,” he told the BBC.

“I think the time has come, the world has changed, Duncan Grant has been gone a long time,” he added. “They need to come out of the closet now and be considered and looked at and thought about. They are a serious collection, as interesting as the erotic drawings on Greek vases and Indian erotic drawings.”