The sexual humiliation of Iraqi prisoners at Abu Ghraib prison was not an invention of maverick guards, but part of a system of ill-treatment and degradation used by special forces soldiers that is now being disseminated among ordinary troops and contractors who do not know what they are doing, according to British military sources.

The techniques devised in the system, called R2I - resistance to interrogation -match the crude exploitation and abuse of prisoners at the Abu Ghraib jail in Baghdad.

One former British special forces officer who returned last week from Iraq, said: "It was clear from discussions with US private contractors in Iraq that the prison guards were using R2I techniques, but they didn't know what they were doing."

He said British and US military intelligence soldiers were trained in these techniques, which were taught at the joint services interrogation centre in Ashford, Kent, now transferred to the former US base at Chicksands.

"There is a reservoir of knowledge about these interrogation techniques which is retained by former special forces soldiers who are being rehired as private contractors in Iraq. Contractors are bringing in their old friends".

Using sexual jibes and degradation, along with stripping naked, is one of the methods taught on both sides of the Atlantic under the slogan "prolong the shock of capture", he said.

Female guards were used to taunt male prisoners sexually and at British training sessions when female candidates were undergoing resistance training they would be subject to lesbian jibes.

"Most people just laugh that off during mock training exercises, but the whole experience is horrible. Two of my colleagues couldn't cope with the training at the time. One walked out saying 'I've had enough', and the other had a breakdown. It's exceedingly disturbing," said the former Special Boat Squadron officer, who asked that his identity be withheld for security reasons.

Many British and US special forces soldiers learn about the degradation techniques because they are subjected to them to help them resist if captured. They include soldiers from the SAS, SBS, most air pilots, paratroopers and members of pathfinder platoons.

A number of commercial firms which have been supplying interrogators to the US army in Iraq boast of hiring former US special forces soldiers, such as Navy Seals.

"The crucial difference from Iraq is that frontline soldiers who are made to experience R2I techniques themselves develop empathy. They realise the suffering they are causing. But people who haven't undergone this don't realise what they are doing to people. It's a shambles in Iraq".

The British former officer said the dissemination of R2I techniques inside Iraq was all the more dangerous because of the general mood among American troops.

"The feeling among US soldiers I've spoken to in the last week is also that 'the gloves are off'. Many of them still think they are dealing with people responsible for 9/11".

When the interrogation techniques are used on British soldiers for training purposes, they are subject to a strict 48-hour time limit, and a supervisor and a psychologist are always present. It is recognised that in inexperienced hands, prisoners can be plunged into psychosis.

The spectrum of R2I techniques also includes keeping prisoners naked most of the time. This is what the Abu Ghraib photographs show, along with inmates being forced to crawl on a leash; forced to masturbate in front of a female soldier; mimic oral sex with other male prisoners; and form piles of naked, hooded men.

The full battery of methods includes hooding, sleep deprivation, time disorientation and depriving prisoners not only of dignity, but of fundamental human needs, such as warmth, water and food.