Six Scotland Yard detectives could face the sack and criminal charges over claims that they subjected suspected drug dealers to water torture.
Investigators are expected to interview the officers under caution by the end of this month as part of an inquiry into allegations that up to five people had their heads submerged in water containers during raids on two north London houses last November.
An internal report into the allegations by the Yard's Directorate of Professional Standards (DPS), the anti-corruption arm of the Metropolitan Police, used the term "waterboarding" to describe the alleged violence, although it is understood the claims do not relate to an exact copy of the CIA-sanctioned controlled drowning technique that became notorious in Guantanamo Bay.
The five people arrested – Victoria Seabrook, David Nwankwo, Ajah Mpakaboari, Nicholas Oforka and Bernasko Adji – were due to face trial in March on charges of importing cannabis.
During a police raid of houses in Enfield and Tottenham on 4 November, Mr Nwankwo, 24, is understood to have told a friend that officers thrust his head down a toilet in the house and repeatedly flushed it while he was questioned. Mr Mpakaboari, 33, claimed to have arrived at the police station in Edmonton, north London, with visible signs of having been assaulted. Ms Seabrook and her boyfriend, Mr Oforka, have not made any allegations of maltreatment.
The torture allegations are part of a wider inquiry by the Independent Police Complaints Commission (IPCC) into claims that officers based at Edmonton Police Station fabricated evidence and stole property from suspects.
The investigation, which the Met referred to the IPCC after a complaint from another officer sparked its own inquiry, is potentially the most damaging scandal yet to confront the new Commissioner, Sir Paul Stephenson. A Met source said: "This is just about as bad as it gets in terms of allegations. We cannot be seen as torturers."
Such was the seriousness of the allegations that a prosecution of the five suspects, who were charged with illegal importation of cannabis, was abandoned in March at a secret court hearing. A Crown Prosecution Service spokesman said: "We took the decision to offer no evidence in this case at trial as it would not be in the public interest to proceed. To do so would have compromised a wide-ranging criminal investigation into a number of police officers."
The Yard said it was taking a tough approach to the allegations. Sir Paul has introduced a new doctrine of "intrusive supervision" in the Met and it is understood the DPS investigation involved the bugging and surveillance of officers in the Edmonton police station.
It was announced yesterday that the Enfield borough commander, Chief Superintendent Adrian Hanstock, had been transferred to Scotland Yard in a new role. There is no suggestion he was implicated in the alleged wrongdoing.
In March, he downplayed the nature of the corruption inquiry, which at that time was focused on property claims, saying it was not of the level portrayed in a BBC drama about 1970s policing.
He said: "We're not talking about Life On Mars-style corruption. This is about procedural compliance."
If the accusations are proven against the officers, who are of detective sergeant rank or below and have been suspended or placed on restricted duties since February, the sanctions available to the Yard include summary dismissal. Once the IPCC investigation is complete, a report will be sent to the Crown Prosecution Service stating whether evidence exists for criminal charges.
The IPCC said it had conducted house-to-house enquiries at the two addresses which were searched on 4 November last year. A spokesman said: "This is an ongoing criminal investigation and as such all six officers will be criminally interviewed under caution."
Jenny Jones, from the Metropolitan Police Authority, said: "The police should be a public protector, ensuring community safety, not an organisation that uses criminal torture tactics."
Turbulent times: Sir Paul Stephenson
28 November 2008 Shadow Immigration minister Damian Green is arrested at the Commons during an investigation into leaked Whitehall documents. Sir Paul, then deputy commissioner, sanctioned the arrest.
1 January 2009 Following the resignation of Sir Ian Blair, Sir Paul is appointed Met Commissioner.
13/26 March The Yard refers its investigations into two serial rapists, taxi driver John Worboys and football coach Kirk Reid, to the IPCC after it emerges opportunities were missed to arrest both men.
1 April Protests at the G20 summit lead to multiple allegations of police brutality and a manslaughter inquiry following the death of Ian Tomlinson.
9 April Assistant Commissioner Bob Quick, Britain's most senior counter-terrorism officer, resigns after he is photographed with secret documents.
10 June Corruption probe launched following torture claims.