The minister for veterans’ affairs, Johnny Mercer, has been given 10 days to reveal the source of allegations British troops engaged in war crimes in Afghanistan, or face a potential prison sentence. Mercer in effect admitted last month in front of the public inquiry into the claims that he believed members of the SAS had engaged in dozens of unlawful killings of Afghan civilians between 2010 and 2013. But he repeatedly refused to hand over names of “multiple officers” who he claimed told him about allegations of murder and a cover-up during his time as a backbench MP. Mercer has yet to state publicly whether he will comply with an order issued by Lord Justice Haddon-Cave, the chair of the Afghanistan inquiry, but a former head of the British army said on Tuesday that the minister was working to get the consent of whistleblowers to pass on their names. The inquiry chair told him last month that his decision to “refuse to answer legitimate questions … at a public inquiry” were “disappointing … surprising … and completely unacceptable”. Haddon-Cave has given Mercer until 5 April to provide a witness statement containing the names. The minister was served with a section 21 notice on 13 March, according to the inquiry, compelling him to hand over the names, which the inquiry said would be treated in confidence. Gen Lord Dannatt, who was the army’s chief of the general staff from 2006 to 2009, said on Tuesday: “Minister Mercer is not withholding the names of his sources from the inquiry because he believes there is a risk the information could be exposed, as the inquiry seems to think. “These whistleblowers came to minister Mercer in confidence and have not given minister Mercer permission to hand over their names, which is why he has not done so. The minister is working on getting their consent. Minister Mercer believes it is fundamentally important that he maintains the trust that whistleblowers can speak to MPs in confidence.” There was also support for Mercer from Robert Campbell, a former British soldier who was cleared in 2020 over the death of an Iraqi teenager after 17 years of investigations, who said the minister’s position in relation to the inquiry was about the public interest of whistleblowers being assured they could speak to figures of authority in confidence. Campbell said he had been “failed” by the chain of command and “utterly abused” by the judicial system during the Iraq Historic Allegations Team investigations, adding: “The last safety net for service personnel when they have nowhere left to turn is to speak to an MP.” The inquiry chair said in the order to Mercer that the consequences of failing to comply without reasonable excuse would be a criminal offence punishable with imprisonment and/or a fine. He also said the high court could enforce the order through contempt of court proceedings, which “may result in imprisonment”. Mercer has until 3 April to lodge an appeal with Haddon-Cave if he wants to claim that he is unable to comply with the notice, or that it is unreasonable for him to do so. The inquiry said in a statement on Monday that it had “robust and sophisticated procedures” in place to protect the identity of potential witnesses, and that Mercer had been given assurances about this on a number of occasions. The judge had previously told the minister: “You need to decide which side you are really on, Mr Mercer. Is it assisting the inquiry fully … and the public interest and the national interest in getting to the truth of these allegations quickly, for everyone’s sake, or being part of what is, in effect … a wall of silence – and this wall of silence is obstructing the inquiry and access to the truth.” The former army officer told the inquiry he had gradually become aware of the SAS allegations, starting with “an odour and pallor” that dated to his last tour of duty in Afghanistan in 2010, followed by at least two specific warnings colleagues gave him in 2017 after became an MP. He acknowledged that, as an MP in 2017, he had been given two warnings by military friends about the seriousness of the allegations. One was described as a senior officer who warned him about the scale of the official investigation into SAS summary killings. The second was a former fellow soldier who said he had been asked to carry a “dropped weapon” that would be used to fabricate evidence of an attack on the elite soldiers and justify civilian killings on night raids in Helmand province.