MPs said on Sunday they might have been misled by the government and a senior military figure over the use of banned interrogation techniques by British troops in Iraq.
The Joint Committee on Human Rights, made up of MPs and peers, said that soldiers had used "conditioning" techniques such as hooding prisoners and putting them in stress positions despite such methods being prohibited.
They argued that conflicted with statements made by former Armed Forces Minister Adam Ingram and Lieutenant General Robin Brims that troops were fully aware that such techniques were banned.
An investigation into the death of Baha Mousa, a 26-year-old hotel worker in the southern Iraqi city of Basra who was beaten to death in British custody in 2003, found some soldiers had employed the banned practices.
Last year, British soldier Corporal Donald Payne pleaded guilty to inhumane treatment at a court martial, after which the head of the army General Sir Richard Dannatt said Mousa and others had suffered unlawful treatment.
Earlier this month the MoD agreed to pay nearly 3 million pounds in compensation to Mousa's family and other Iraqis beaten and tortured by British troops in 2003.
"We have yet to receive an explanation from the Ministry of Defence (MoD) for the discrepancies in evidence given to the committee by Mr Ingram in 2004 and Lieutenant General Brims in 2006 on the use of these illegal conditioning techniques," the committee chairman Andrew Dismore said in a statement.
Defence Secretary Des Browne said there would be a public inquiry into Mousa's death which would also examine the issue raised by the committee.
"We acknowledge that in 2003, some of the conditioning techniques were used on a small number of detainees," Browne said in a statement.
"This should not have happened and we need to know how it came about. That is why I endorse the terms of the Inquiry wholeheartedly."
He said since 2003 there had been "considerable improvements" made in the training of soldiers about the treatment of detainees.
