Several former detainees have said they have been tortured, with the knowledge of British intelligence officers, while held abroad.

'Complicity' in torture

Britain has intensified foreign intelligence efforts since suicide bombers, said to have received training in Pakistan, killed 52 passengers on London's public transport system in 2005.

But rights groups have criticised the government for not acting more effectively against ill-treatment of detainees held by allies.

A parliamentary committee report released on Sunday also accused the government of not sufficiently addressing its alleged involvement in the torture of suspects held overseas.

The report, which raised concerns over Britain's co-operation with Pakistan's Inter-Services Intelligence Agency (ISI), called for an independent inquiry.

"While the UK must, by necessity, maintain its relationship with Pakistani intelligence, we are very concerned by allegations that the nature of the relationship UK officials have with the ISI may have led them to be complicit in torture," the report said.

The report also warned the government that continuing to use information from foreign intelligence agencies that had ignored past British requests to stop torturing suspects could constitute collusion in torture.

"Use of evidence which may have been obtained under torture on a regular basis, especially where it is not clear that protestations about mistreatment have elicited any change in behaviour by foreign intelligence services, could be construed as complicity in such behaviour," the report said.