The vivid purple scars on his chest and feet, inflicted he says by President Mugabe’s security forces, show why church leaders and human rights groups are demanding an end to the forcible return of Zimbabwean asylum-seekers.

Usher’s story of his torture since his expulsion in May is the first detailed account of what lies in store for some of those returned. It challenges Charles Clarke’s statement to MPs last week that, to the knowledge of the Home Office, none of the asylum-seekers sent back to Zimbabwe has come to any harm. Refugee organisations say that they have been unable to trace most of the deportees. Those whom they have tracked down are too scared to say anything publicly about their treatment.

As the hunger strike by Zimbabweans in British detention centres entered its 13th day, Usher told The Times: “Anyone sent back here after running away to Britain is in terrible danger, and those helping us are at great risk.”

Usher, 24, fled to Britain in November 2002 after police tortured him in an attempt to make him reveal the whereabouts of his uncle, an activist for the Movement for Democratic Change opposition party in Zimbabwe’s Eastern Highlands. He was given exceptional leave to remain and went to live with his aunt Mary in Brixton, South London.

He was staying with his English-born girlfriend in Sussex when at the end of April he was asked to report to immigration officials in London. “I was told it was a routine meeting. This time though I was asked to wait in a room with five other Zimbabwean men,” he said.

Without warning or explanation he and the others were taken to Harmondsworth detention centre, near Heathrow. Before his family or lawyers could intervene, Usher was transferred to Dover and, nine days after his arrest, was forced on to an aircraft in handcuffs with another asylum-seeker.

At Harare airport Usher’s British escorts, working for a private security company on contract to the Home Office, handed the pair over to police.

“We were punched on the head and neck and asked why we didn’t have the right travel documents. Then four agents from what we took to be the Central Intelligence Organisation appeared and we were moved to separate rooms. They kicked me and kept shouting that I was a British spy.”

After two days of interrogation, Usher was driven to the central prison in Harare, where he was repeatedly beaten on the soles of his feet. Over the next three weeks in custody he says that he was subjected to electric shock treatment to his chest and testicles.

“They told me I would suffer for going to England,” he said.

Last month he appeared in a Harare court with other deportees and magistrates warned them that they faced charges carrying long prison sentences. As they were led from the dock one official thought that Usher had been given bail, and he took his chance to escape.

He says that for much of the past three weeks he has lived in the bush, scavenging for food, until a school friend took him in. “If I am captured again they will kill me for sure,” he said. “I believe Tony Blair and his ministers cannot know what is happening here or they would not send people back. My only hope now is to somehow get across the border.”

Worried family and friends have tried in vain to alert the British authorities to Usher’s plight. His aunt Mary, who has looked after him since his parents died, said: “He wanted to study art here. He was never in trouble, he was respectful and loving and now I don’t know what is happening to him.”

She was allowed to see him only once during his detention.

“How can Mr Blair talk of human rights at his G8 summit and send boys like this back to danger? The Government is turning its back on murder.”

The Home Office said last night that it did not routinely monitor the returnees and suggested that Usher contact the High Commission in Harare.

Kate Hoey, his local MP, said: “Nobody is looking out for deportees like Usher. Once they are out of Britain the HO couldn’t give two hoots.”

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