A former SAS soldier claimed today that the British secret service had been operating in a covert joint squad with the United States in Iraq and Afghanistan since 2001 and that UK operatives knew detainees were being tortured by the Americans.

Ben Griffin, 29, who left the military at the beginning of last year, said British political leaders knew about what went on in the taskforce and were therefore complicit in the "illegal" tactics being used by US troops. He called for Tony Blair and Gordon Brown to face trial for breaking international law.

The former serviceman, who said he left the forces on "moral" grounds, told a press conference today that, since the invasion of Afghanistan in the autumn of 2001, UK special forces had operated within a joint secret American-British unit.

“This task force has been responsible for the detention of hundreds, if not thousands, of individuals in Afghanistan and Iraq,” Mr Griffin told an event hosted by the Stop the War Coalition.

The Foreign Office refused to comment on the allegations, but referred journalists back to the Government's statement last week. In it, David Miliband told MPs that Britain had recently been made aware of two US extraordinary rendition flights which had stopped off in the British Indian Ocean island territory of Diego Garcia in 2002 to refuel.

The Government claims that, before the recent US admission about Diego Garcia, it did not know that America used British soil for so-called "torture flights" and had no knowledge of alleged American military torture.

Mr Griffin claimed that, while the Government had stated its desire that the Guantanamo Bay camp be closed, it had remained silent over other secretive prisons in Iraq and Afghanistan where individuals faced torture and were held indefinitely without charge.

“Throughout my time in Iraq I was in no doubt that individuals handed over to our American colleagues would be tortured,” he added. “I have no doubt in my mind that non-combatants I personally detained were handed over to the Americans and subsequently tortured.”

He added: “British soldiers are intimately involved in the actions of this task force. Jack Straw, Margaret Beckett, David Miliband, Geoff Hoon, Des Browne, Tony Blair, Gordon Brown - in their respective positions over the last five years they must know that British soldiers have been operating within this joint US/UK task force. They must have been briefed on the actions of this unit.

“It is only since I have left the Army - that I have read the Geneva Convention and the UN Convention on Torture - that I realised that we have broken so many of these conventions and treaties in Iraq. They should be charged with breaching these conventions.

“They must have had knowledge of what was going on, they have allowed it to happen, so I would like the lot of them charged.”

In a statement, a Foreign Office spokesman said: "We are not commenting on these allegations at all, except to refer you to the Foreign Secretary's statement last week."

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