A former soldier who had kept his silence for six years broke ranks yesterday to accuse his superior officer and former comrades of the brutal beating and torture of Iraqi prisoners which ended in the killing of an Iraqi civilian.

Donald Payne, 35, a former corporal in the British Army, said that the soldiers had acted out of revenge over the murder of three Royal Military Policemen and the killing of an Army captain who had been blown up while delivering humanitarian aid to southern Iraq.

In a dramatic change to his evidence, Payne, who has already been convicted of the inhumane treatment of Iraqis, told a public inquiry he and other soldiers had routinely kicked and punched nine Iraqi detainees captured in September 2003. One of them, Baha Mousa, died from asphyxiation and 93 separate injuries. The new allegations raise concerns about the widespread abuse of dozens of Iraqi detainees and come days after the Ministry of Defence said it was investigating 33 other separate cases of torture carried out by British soldiers in Iraq and revealed in The Independent on Saturday.

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Payne also claims an officer, Lt Craig Rodgers, subjected one of the detainees to a mock execution by forcing him to the ground and pouring liquid over him so that he believed he was to be set on fire. In a separate incident, Payne says he saw his commanding officer, Lt-Col Jorge Mendonca, interrogate a captured Iraqi by placing a cocked pistol above the man's mouth before telling him he intended to "blow his face off".

Last night lawyers representing the family of Baha Mousa called on the prosecuting authorities to bring murder charges against those responsible for Mr Mousa's death. Phil Shiner of Public Interest Lawyers said: "At long last Donald Payne has decided to tell the truth. Nobody faced charges for murder or torture in the hopelessly flawed military prosecution and all those responsible should now be charged with murder."

Sapna Malik of law firm Leigh Day and Co added: "Donald Payne's latest evidence... shows the vital role played by the inquiry in getting closer to establishing the truth of what happened to Baha Mousa and his colleagues during those fatal hours and again highlights the deep flaws of the military police investigation and court martial process."

In 2006 Payne became the first member of the UK armed forces to be convicted of a war crime when he pleaded guilty at a court martial to inhumanely treating the Iraqi civilians.

He was part of a group, headed by Lt Rodgers, known by the call sign G10A.

Payne sat with his back to the public gallery. He told the inquiry's chairman Sir William Gage, that he had covered up the extent of the abuse of Iraqis by British soldiers out of "misguided loyalty". He previously claimed he had only nudged or slapped detainees and never saw them being beaten by their guards. In a statement, Payne, who joined the Army in June 1988, told the inquiry: "I have known the disclosures I am about to make would harm the reputation of both my former regiment and the British Army and for these reasons have so far been unwilling to make them even to my lawyers.

"I now disclose that in adopting the routine I did, each time I returned to the temporary detention facility to ensure the detainees were awake, the degree of force I applied was greater than I have so far admitted."

He added: "Moreover at one time or another I saw all the members of the multiple in call sign G10A emulate me."

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Payne admitted that he lied "about almost everything" in interviews conducted during 2003 and 2004, had lied to the court martial and in his first statement to the public inquiry for reasons of "self-preservation".

He agreed with Gerard Elias QC, counsel to the inquiry, that the force he had used had actually amounted to "an element of gratuitous violence".

The former soldier suggested he beat the detainees because he believed – wrongly – that they were linked to the deaths of three Royal Military Police soldiers in Iraq in June 2003.

Payne, who had served several tours of duty in Northern Ireland and had been in Omagh on the day of the IRA bombing, said it was the false "rumour" that Mr Mousa and the other detainees could have been responsible for killing the RMPs that triggered the violence. He claims the "rumour" was passed to him by Major Michael Peebles.

Mr Elias asked: "What did he tell you in that context?

Payne replied: "These could be the guys that had done the RMPs."

Mr Elias then asked: "was it the case, for example, that you believed that they were involved in some previous killing?"

"Maybe, yes," answered the former soldier with a dismissive shrug of his shoulders.

"Was that something that had anything to do with your behaviour?

"Yes," answered Payne.

A week after the death of Mr Mousa, Payne said he had a conversation with Lt-Col Mendonca. "He told me that the incident would mean the end of his career and mine. The impression I gained was that he was going to try and cover his own back if necessary, at the expense of mine."

Payne also said in a statement to the inquiry: "It was my impression that the CO [commanding officer] was trigger happy. He would pull his pistol out at any opportunity. He would behave as if he were a member of the SAS." Lt-Col Mendonca, who was later promoted to colonel before leaving the Army in 2007, was charged with negligently performing a duty and with five other soldiers was cleared at the court martial. His counsel, Tim Langdale QC, accused Payne of telling lies about his client.

Mr Rodgers, who left the Army in March 2007 having reached the rank of captain, strongly denied allegations of prisoner abuse when he gave evidence to the inquiry last week. He said in a witness statement: "I did not hit, punch, kick or physically assault any of the detainees at any time."

The inquiry continues today.