No collusion

Evans admitted that British intelligence was "slow to detect" US mistreatment of detainees after the September 11, 2001, attacks on America.

But he said: "We in the [British] agencies did not practise mistreatment or torture then and do not do so now, nor do we collude or encourage others to torture on our behalf."

Judges handed down the ruling as they ordered the release of once-secret information about the case of Mohamed, which showed he had been subject to abuse at the hands of US authorities. 

The CIA had passed the information to British intelligence, and judges released it after David Miliband, the British foreign minister, lost a court appeal for it not to be released.

The judges rejected the UK government's claim that disclosing the information would damage intelligence co-operation with US agencies.

The publication of the seven-paragraph summary showing the UK was aware of the US authorities' abuse, combined with the judge's criticism, has intensified arguments in the UK about MI5's alleged attempts to conceal its collusion in torture.

'Propaganda' opportunity

Evans also warned that Britain's enemies could use the escalating row as "propaganda to undermine our will and ability to confront them".

Ethiopian-born Mohamed, who came to Britain in 1994 seeking asylum, claims that in Morocco in 2002 he was questioned by people using information that could only have come from the British intelligence service.

Miliband disclosed on Wednesday that police were investigating allegations of criminal actions by a British official linked to the case. 

Mohamed was arrested in Pakistan in 2002 while trying to return to Britain and spent nearly seven years in US custody or in countries taking part in the US-run rendition programme of terrorism suspects.

After a lengthy campaign by his supporters, he became the first prisoner to be released from Guantanamo under the administration of Barack Obama, the US president, and returned to Britain in February last year.