UNITED Nations human rights investigators have concluded the British government has been complicit in the mistreatment and possible torture of several of its own citizens during the “war on terror”.

In a report published on Wednesday that will make difficult reading for British ministers who repeatedly denied the UK's involvement in torture, UN officials have indicated there is clear evidence of the UK's role in the secret detention overseas of several British Muslims.

The officials say such secret imprisonment — or “proxy detentions” — not only facilitates torture, but may amount to torture in its own right. In one starkly worded passage, they warn that if a state's use of proxy detention had been systematic or widespread it would amount to a “crime against humanity”.

There was no immediate comment from the British government.

The 226-page UN report follows the publication two months of ago a dossier entitled Cruel Britannia, from the New York-based NGO Human Rights Watch, whose researchers interviewed several Pakistani intelligence agents who alleged they had tortured British terrorism suspects on behalf of their UK counterparts.

It also follows a series of disclosures in the Guardian about the role played by officers of MI5 (British security service), MI6 (British intelligence) and Greater Manchester police, in the north of England, in the detention and questioning under torture of terrorism suspects held in Pakistan and elsewhere.

The UN investigation into torture and rendition across the globe since 9/11 lasted several years and was led by Martin Scheinin, UN special rapporteur on terrorism and human rights, and Manfred Nowak, special rapporteur on torture.

In a move that will do little to ease the discomfort of western governments that were the focus of the investigation, the two men and their aides were assisted by members of a UN working party on secret detentions first set up in 1979 to investigate the fate of people who were “disappeared” by the Pinochet regime in Chile.

Their report concludes that secret detention “amounts to a case of enforced disappearance” and that it is “a manifold human rights violation that cannot be justified under any circumstances, including during states of emergency”.

Listing those cases in which they conclude that a state has been complicit in a secret detention, the authors highlight “the United Kingdom in the cases of several individuals, including Binyam Mohamed, Salahuddin Amin, Zeeshan Siddiqui, Rangzieb Ahmed and Rashid Rauf”.

Ahmed, 34, from Rochdale, Greater Manchester, was detained in Pakistan in 2006. MPs have heard that after evidence of his terrorist offences had been gathered he was allowed to fly from Manchester to Islamabad, and that MI6 then suggested to a Pakistani intelligence agency that its officers should detain him as he was a dangerous terrorist.

— The Guardian, London