Boris Johnson's Defence Secretary Ben Wallace has appeared to condoned mock executions in a 2003 interview to the Scotsman.
"You might pretend to pour petrol over them, when it's actually water," he said, describing how prisoners are manhandled by soldiers, "to give them an idea of the seriousness."
The comments were discovered by the human rights NGO Reprieve and published in the Guardian yesterday.
Director of Reprieve Maya Foa said: "It's hard to see why Mr Wallace would pretend he was pouring petrol on a detainee other than to make them think they were about to be burned alive, which quite obviously amounts to a mock execution."
After the "war on terror" which followed the September 11 terror attack, the CIA kidnapped terror suspects and tortured them at "black sites" or in the countries of "friendly" dictators.
Referred to by the CIA as "enhanced interrogation techniques", mock executions were used alongside the threat of rape or to harm a prisoner's children.
In 2014 a US Senate report labelled them brutal and ineffective and concluded that the CIA lied about how useful they were, finding that torture regularly led to fabricated information.
The European Convention on Human Rights and the Ministry of Defence's Joint Doctrine publication prohibits torture, however, Wallace argued in 2003 that mock executions are necessary to get the most amount of information in the swiftest manner possible.
"I would defend the right of soldiers to interrogate at the point of capture, swiftly and sharply because that's when you get the most information."
"That is not a war crime. Where there's still a threat to our forces, you need to know information quickly. If that man had been given a cup of tea, would he really have told about his weapons under the floor?"
Foa said: "The behaviour Mr Wallace is endorsing is not simply ineffective, it is illegal, immoral, and undermines principles which generations of British service personnel risked their lives to protect."
Despite the fact that there is strong evidence that the UK was involved in torture and extraordinary rendition post 9/11, earlier this year the Conservative government under Theresa May said it would not set up an independent, judge-led inquiry into the UK's role.