Donald Trump has said he will leave the decision on whether the US should use torture to his Defence Secretary, Gen James Mattis.

During the presidential campaign, Mr Trump said he wanted to make use of waterboarding as part of the fight against extremists, including Isis.

As recently as this week, he told an interviewer not only that he believed that “torture worked” but that the intelligence officials advising him did so too – a claim that spark widespread debate among among security experts.

At a news conference on Friday with Prime Minister Theresa May, Mr Trump repeated his belief in the value of torture. Yet he said he would leave the decision on whether or not to use it, up to his Defence Secretary, Mr Mattis, whom he described as a “general’s general”.

“He has stated publicly that he does not necessarily believe in torture or waterboarding, or however you want to define it… I don’t necessarily agree,” said Mr Trump.

“But I would tell you that he will override because I’m giving him that power. He’s an expert.”

During his Senate confirmation hearing, Mr Mattis opposed the use of torture.

The Associated Press said that Mr Trump once quoted Mr Mattis as saying: “Give me a pack of cigarettes and a couple of beers and I do better with that than I do with torture.”

The Senate passed a ban on torture in 2015, but Mr Trump’s public comments have led to concerns that he may try to bring it back. In an ABC News interview this week, Mr Trump said that he believed torture “absolutely” works.

“I’ve spoken as recently as twenty-four hours ago, with people at the highest level of intelligence, and I asked them the question,” Mr Trump said.

“Does it work? Does torture work? And the answer was yes. Absolutely.”

He said he would leave the decision on whether to use torture to Mr Mattis and the new CIA director, Mike Pompeo.

He added: “If they do want to do it, I will work toward that end. I want to do everything within the bounds of what you’re allowed to do legally. But do I feel it works? Absolutely I feel it works.”

Mr Trump’s comments on Friday will have made things easier for Ms May, The British leader had suggested that British intelligence could stop working with American intelligence if the US reinstated the use of torture.

Others who have spoken out against torture, both from the point of view of human rights and its inefficiency, include Senator John McCain, who was held captive and tortured by North Vietnamese forces during the Vietnam War.