A secret army interrogation unit accused of being responsible for the widespread abuse of Iraqi prisoners is being investigated by the Ministry of Defence.

Fourteen fresh claims of torture against the British Army include detailed accounts of a shadowy team of military and MI5 interrogators who are alleged to have authorised the physical and sexual abuse of Iraqi detainees.

The new allegations bring the total number of cases being investigated by the Government to 47.

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Many of the Iraqis allege they were abused after they were sent to a unit called the Joint Forward Intelligence Team (JFIT) based at the Army's Shaibah Logistics Base, 13 miles from Basra, between 2004 and 2007. Nearly all the men say they were beaten, denied sleep and then dragged around the prison compound before facing multiple interrogations.

In one account the interrogators are accused of creating an image superimposing a suspect's head on the body of a man who is sexually abusing a child, and then threatening to disseminate the image throughout Basra.

In another, a detainee, held in solitary confinement for 36 days, alleges that interrogators threatened to rape his wife and kill his children.

Many of the detainees' witness statements appear to corroborate each other by referring to named soldiers responsible for their alleged torture.

According to the Iraqis' solicitors, Public Interest Law (PIL), the men were all held in solitary confinement in a "compound within a compound" guarded by a specialist detachment of soldiers. The lawyers claim that the JFIT interrogators were a mix of members of the military, MI5 and civilian staff and that they took their orders directly from London.

In 2003 the Americans raised concerns that the British were failing to secure intelligence from Iraqi prisoners held at the UK/US Camp Bucca in southern Iraq who were suspected of having close links with extremist militias. They urged their British counterparts to take a tougher line.

Lawyers and human rights groups now believe the British heeded the Americans' concerns by allowing personnel attached to JFIT to conduct coercive and unlawful interrogations. The Americans were later found to have tortured prisoners held at the Abu Ghraib prison, which has since been renamed the Baghdad Central Prison.

Between 2004 and 2007 hundreds of prisoners were held at the Divisional Temporary Detention Facility compound run by JFIT at the Shaibah base. When the JFIT interrogators had finished with them, the prisoners were released into the camp's main prison halls, where they claim their abuse continued.

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Many of these detainees complain of being subjected to sexual and physical abuse by male and female soldiers. Last year The Independent reported that the Ministry of Defence was investigating 33 separate allegations of abuse.

Phil Shiner, a human rights lawyer who is representing all the detainees, said that the Government must come clean about the role of the JFIT interrogators in the alleged unlawful detention and abuse of Iraqi prisoners.

In a legal letter, setting out the men's claims and sent to the Defence Secretary, Bob Ainsworth, Mr Shiner said: "The forms of ill-treatment suffered by the claimants include physical beatings, deprivation of food, exposure to the cold and excessive heat, threats of rape and violence, sexual humiliation and solitary confinement. It is manifestly clear that the extent and culmination of the above amount to a clear and egregious breach of Article 3 of the European Convention on Human Rights.

"In particular, the allegations evidence a return to the use of coercive interrogation techniques declared unlawful by the European Court of Human Rights (ECtHR) in Ireland vUK (1978) 2 EHRR 25.

"It must also be said that the marked similarity of the claimants' allegations with so many other cases lends a great weight of credibility to the allegations."

He added: "Much of the ill-treatment suffered by the men was clearly intended to break their will for the purpose of interrogation. This is in clear breach of international provisions and in clear breach of ECtHR jurisprudence."

A spokeswoman for the Ministry of Defence said that while she could not comment on any individual cases she was able to confirm that all 47 were or will be investigated.

She also confirmed that JFIT is part of the Army's intelligence corps and that, as for any other military personnel, the allegations made against them will be investigated but "remain allegations until they are proven".

The Armed Forces minister, Bill Rammell, said: "We must never forget that over 120,000 British troops have served in Iraq and the vast, vast majority have conducted themselves to the highest standards of behaviour, displaying integrity and selfless commitment. Only a tiny number have ever fallen short of our high standards, but even a tiny number is unacceptable. All allegations of abuse are taken very seriously. However, allegations must not be taken as fact, and formal investigations must be allowed to take their course without judgements being made prematurely."

Case study: 'A soldier hit me again and again with a hammer for at least three minutes'

In one of the most disturbing cases Hussain Ghazi Shihab, 35, claims he was badly beaten by soldiers before being handed over to specialist interrogators at Shaibah.

He recalls: "The officer showed me another photograph of a man... [and] insisted that I knew where he lived. I told him I did not know, otherwise I would take him there. The more I told them I couldn't help, the more the officer instructed the soldiers to beat me further. The soldiers were hitting me with their fists, kicking me and bringing their rifle butts down on to my head and body. I was hit hard in the stomach by a soldier who had picked up a hammer.

"The pain was horrendous and I fell forward grabbing my stomach in agony. He hit me again and again with the hammer for at least three minutes on different parts of my body, but mainly concentrating on my stomach... I vomited later when I was in the tank and there was blood in the vomit."

The injuries were so serious he claims members of the Joint Forward Intelligence Team were forced to break off the interrogations so he could receive hospital treatment. Mr Shihab, a policeman employed by Iraq's Ministry of Transport in Basra, said the lead interrogator who threatened and abused him during his detention in 2006 was dressed in civilian clothes.

In one of the most shocking allegations made against British soldiers, Mr Shihab alleges the interrogators superimposed his head on the photograph of a man sexually abusing a child.

"The photographs were of Western faces and the people looked to be around 15 to 16 years old," he said. "The sheet of paper was about A4 size and there were around 10 photographs on it. The interrogator told me that I should admit to raping the children in the pictures. He said that if didn't confess he would send information to Basra to say that I was part of a sex gang which kidnapped and raped young girls and then threw them on to the street.

"He said they were just about to send the picture to the police unless I gave them the information they required. They even said they would distribute it on the streets in my area to my neighbours and friends."

Case study: Sleep deprived, kept in the dark, blindfolded

Sajjad Naji Nassir, 40, was arrested at his home by British forces on 18 September 2005 when he claims he was shot in the foot and fell unconscious.

On arrival at Shaibah he was forced into a kneeling stress position on pebbled ground. In a letter to the Ministry of Defence his lawyers allege that he was barefoot and was dressed only in his underwear. If he moved or rested from the stress position a soldier kicked him in the back, he says. Mr Nassir was in this position for three hours before being taken to an interrogation. He estimates that over an eight-hour period he was interrogated eight times before returning to his permanently dark prison cell.

He was held in these conditions for two-and-a-half months, during which time he was interrogated frequently, he says. When Mr Nassir was taken out of his cell he was blindfolded and ear muffed and walked in a disorienting zigzag.

He was deprived of sleep by soldiers making noise and kicking the doors of the cells. Soldiers also allegedly played pornographic movies at high volume, including during Ramadan. He could only eat bread and fruit because the soldiers could not confirm the meat was halal.