Former defence secretary Sir Ben Wallace has rejected claims by ex-veterans’ minister Johnny Mercer that he “lacked curiosity” when responding to allegations of a cover-up of special forces murders in Afghanistan.

Mr Mercer wrote to Sir Ben in August 2020 shortly after emails surfaced in The Sunday Times which showed senior special forces officers expressed serious concerns about the killings of 33 people in 11 night raids in the war-torn nation in 2011.

The former veterans’ minister previously told the Afghanistan Inquiry he was “angry” with Sir Ben, as well as the director of special forces and the chief of the general staff, because they had “not done their job that was incumbent upon them with their rank and privileges in those organisations”.

Hitting back at Mr Mercer’s claims on Monday, the former defence secretary described the claims that he lacked curiosity as “highly inaccurate”, adding: “I was absolutely inquisitive.”

The inquiry is examining whether a special forces unit, known to the probe as UKSF1, had a policy of executing males of “fighting age” who posed no threat in Afghanistan between 2010 and 2013.

Afghan families have accused UK special forces of conducting a “campaign of murder” against civilians, while senior officers and personnel at the Ministry of Defence “sought to prevent adequate investigation”.

Questioning Sir Ben, counsel to the inquiry Oliver Glasgow KC said: “Mr Mercer described in his evidence to the inquiry that he thought you lacked curiosity when it came to responding to some of the allegations that he brought to your attention – is that a description of your attitude towards what he said to you, is it an accurate one?”

The former defence secretary replied: “I think it’s highly inaccurate.

“I think my actions, if you look at my statement, are the entire opposite of that.

“Not only did I seek to dig deeper, I also even sought to dig internationally whether or not the assurances I’d been given were truthful.

“Secondly, I established this inquiry… so I was absolutely inquisitive.

“I held the department to account if I felt that they were not producing what we had asked for.

“But I also had to reiterate that we had to act on the evidence before us, and that I also have a duty to the men and women of the armed forces to make sure that their reputation is not dragged through the mud or indeed libelled or besmirched without evidence.”

Sir Ben was also questioned on a missive sent by director of judicial engagement policy Peter Ryan in 2019, which concluded that allegations of special forces murders were “broadly accurate”.

Mr Glasgow asked: “Is that the sort of submission that one needs to pay attention to, Sir Ben?”

The former defence secretary replied: “I did pay attention to it – we are sitting in a public inquiry to get to the bottom of it.”

Questioned on whether he was worried that the allegations had been judged to be “broadly accurate”, Sir Ben said: “I’ve said, I’ve never strayed from my belief that there may be more evidence out there.”

Two Royal Military Police investigations, codenamed Operation Northmoor and Operation Cestro, are also being scrutinised by the inquiry.

No charges were brought under Operation Northmoor – a £10 million investigation which was set up in 2014 to examine allegations of executions by special forces, including those of children.

Operation Cestro saw three soldiers referred to the Service Prosecuting Authority, but none of them were prosecuted.

The inquiry continues.