A shocking new report alleges widespread complicity between British security agents and their Pakistani counterparts who have routinely engaged in the torture of suspects.

In the study, which will be published next month by the civil liberties group Human Rights Watch, at least 10 Britons are identified who have been allegedly tortured in Pakistan and subsequently questioned by UK intelligence officials. It warns that more British cases may surface and that the issue of Pakistani terrorism suspects interrogated by British agents is likely to "run much deeper".

The report will further embarrass the foreign secretary, David Miliband, who has repeatedly said the UK does not condone torture. He has been under fire for refusing to disclose US documents relating to the treatment of Guantánamo detainee and former British resident Binyam Mohamed. The documents are believed to contain evidence about the torture of Mohamed and British complicity in his maltreatment. Mohamed will return to Britain this week. Doctors who examined him in Guantánamo found evidence of prolonged physical and mental mistreatment.

Ali Dayan Hasan, who led the Pakistan-based inquiry, said sources within the country's Inter-Services Intelligence agency (ISI), the Intelligence Bureau and the military security services had provided "confirmation and information" relating to British collusion in the interrogation of terrorism suspects.

Hasan said the Human Rights Watch (HRW) evidence collated from Pakistan intelligence officials indicated a "systemic" modus operandi among British security services, involving a significant number of UK agents from MI5 rather than maverick elements. Different agents were deployed to interview different suspects, many of whom alleged that prior to interrogation by British officials they were tortured by Pakistani agents.

Among the 10 identified cases of British citizens and residents mentioned in the report is Rangzieb Ahmed, 33, from Rochdale, who claims he was tortured by Pakistani intelligence agents before being questioned by two MI5 officers. Ahmed was convicted of being a member of al-Qaida at Manchester crown court, yet the jury was not told that three of the fingernails of his left hand had been removed. The response from MI5 to the allegations that it had colluded in Ahmed's torture were heard in camera, however, after the press and the public were excluded from the proceedings. Ahmed's description of the cell in which he claims he was tortured closely matches that where Salahuddin Amin, 33, from Luton, says he was tortured by ISI officers between interviews with MI5 officers.

Zeeshan Siddiqui, 25, from London, who was detained in Pakistan in 2005, also claims he was interviewed by British intelligence agents during a period in which he was tortured.

Other cases include that of a London medical student who was detained in Karachi and tortured after the July 2005 attacks in London. Another case involving Britons allegedly tortured in Pakistan and questioned by UK agents involves a British Hizb ut-Tahrir supporter.

Rashid Rauf, from Birmingham, was detained in Pakistan and questioned over suspected terrorist activity in 2006. He was reportedly killed after a US drone attack in Pakistan's tribal regions, though his body has never been found.

Hasan said: "What the research suggests is that these are not incidents involving one particular rogue officer or two, but rather an array of individuals involved over a period of several years.

"The issue is not just British complicity in the torture of British citizens, it is the issue of British complicity in the torture period. We know of at least 10 cases, but the complicity probably runs much deeper because it involves a series of terrorism suspects who are Pakistani. This is the heart of the matter.

"They are not the same individuals [MI5 officers] all the time. I know that the people who have gone to see Siddiqui in Peshawar are not the same people who have seen Ahmed in Rawalpindi."

Last night the government faced calls to clarify precisely its relationship with Pakistan's intelligence agencies, which are known to routinely use torture.

A Foreign Office spokesman said that an investigation by the British security services had revealed "there is nothing to suggest they have engaged in torture in Pakistan". He added: "Our policy is not to participate in, solicit, encourage or condone the use of torture, or inhumane or degrading treatment, for any purpose."

But former shadow home secretary David Davis said the claims from Pakistan served to "reinforce" allegations that UK authorities, at the very least, ignored Pakistani torture techniques.

"The British agencies can no longer pretend that 'Hear no evil, see no evil' is applicable in the modern world," he added.

Last week HRW submitted evidence to parliament's Joint Committee on Human Rights. The committee is to question Miliband and Jacqui Smith, the home secretary, over a legal loophole which appears to offer British intelligence officers immunity in the UK for any crimes committed overseas.

It has also emerged that New York-based HRW detailed its concerns in a letter to the UK government last October but has yet to receive a response.

The letter arrived at the same time that the Attorney General was tasked with deciding if Scotland Yard should begin a criminal investigation into British security agents' treatment of Binyam Mohamed. Crown prosecutors are currently weighing up the evidence.

Hasan said that evidence indicated a considerable number of UK officers were involved in interviewing terrorism suspects after they were allegedly tortured. He told the Observer: "We don't know who the individuals [British intelligence officers] were, but when you have different personnel coming in and behaving in a similar fashion it implies some level of systemic approach to the situation, rather than one eager beaver deciding it is absolutely fine for someone to be beaten or hung upside down."

He accused British intelligence officers of turning a blind eye as UK citizens endured torture at the hands of Pakistan's intelligence agencies.

"They [the British] have met the suspect ... and have conspicuously failed to notice that someone is in a state of high physical distress, showing signs of injury. If you are a secret service agent and fail to notice that their fingernails are missing, you ought to be fired."

Britain's former chief legal adviser, Lord Goldsmith, said that the Foreign Office would want to examine any British involvement in torture allegations very carefully and, if necessary, bring individuals "to book" to ensure such behaviour was "eradicated".