LONDON, ENGLAND - The head of Britain's domestic spy service, which is accused of colluding with torture, has defended working with foreign agencies that have different values, saying the collaboration has saved lives.

MI5 director-general Jonathan Evans admitted his service faced a "real dilemma" about working with foreign security forces whose standards "were very far removed from our own", but said such cooperation helped keep Britain safe.

British police are currently investigating allegations that MI5 colluded in the torture of Binyam Mohamed, a former inmate of the US detention centre at Guantanamo Bay, following his arrest in Pakistan in 2002.

In a speech to the University of Bristol in western England late Thursday, Evans said he could not comment directly on the allegations, but insisted "the security service does not torture people, nor do we collude in torture".

He said that after the threat of Al Qaeda emerged following the September 11, 2001, attacks on the United States, Britain's intelligence services were ill-equipped to deal with the threat and had to look for help elsewhere.

"Our intelligence resources were not adequate to the situation we faced and the root of the terrorist problem was in parts of the world where the standards and practices of the local security apparatus were very far removed from our own," Evans said.

"This posed a real dilemma. Given the pressing need to understand and uncover Al Qaeda's plans, were we to deal (however circumspectly) with those security services who had experience of working against At Qaida on their own territory, or were we to refuse to deal with them."

Such a refusal "would be cutting off a potentially vital source of information that would prevent attacks in the West", he said, and in doing so the agency "would have been derelict in our duty" to protect national security.

Evans said he had "every confidence in the behaviour of my officers" and stressed that many lives had been saved.

"Many attacks have been stopped as a result of effective international intelligence co-operation since 9/11," he said.