Defence chiefs and ministers face fresh pressure over the treatment of civilians at the hands of British forces in Iraq today, as a new report revives fears that "torture" techniques have been used 30 years after they were banned.

A scathing report from the Joint Human Rights Committee (JHRC) warns that the use of "coercive interrogation techniques" may have been officially sanctioned, despite assurances that troops knew they were outlawed.

The former armed forces minister Adam Ingram and Lieutenant-General Robin Brims, former Commander Field Army, told an earlier committee inquiry that British forces knew they could not use five "conditioning" techniques – wall standing, hooding, subjection to noise, and deprivation of sleep, food and drink – during interrogation.

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But the committee has now ruled that their evidence conflicts with the findings of a subsequent court-martial hearing, and an internal Ministry of Defence review into the death of an Iraqi hotel worker, Baha Mousa, at the hands of British soldiers in September 2003.

The JHRC report also found that the use of hooding and stress positioning by 1 Queen's Lancashire Regiment in 2003 was based on legal advice received from brigade headquarters. It claims that, at least until the Baha Mousa case came to light, the prohibition on the use of conditioning techniques "was not as clearly articulated to troops in Iraq as it might, and indeed should, have been".

The committee's chairman, Andrew Dismore, said: "We have yet to receive an explanation from the Ministry of Defence for the discrepancies in evidence given ... by Mr Ingram in 2004 and Lieutenant-General Brims in 2006 on the use of these illegal ... techniques."

Phil Shiner of Public Interest Lawyers, who has represented Iraqis who claim abuse at the hands of British troops, said: "We are meant to believe that it is just ... a few bad apples, but the evidence from courts martial and other cases shows that nothing could be further from the truth. These methods are about breaking people down. They were meant to have been banned, but somehow they came back and they became written and verbal policy."