Mr Mercer, the veterans minister, is potentially facing time in prison over his decision not to hand over the information to the Independent Inquiry relating to Afghanistan.

The former soldier was asked several times by the inquiry chair, Sir Charles Haddon-Cave, to name the people who told him about the alleged killings by UK troops.

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But Mr Mercer refused to do so on the basis that he did not have the permission of his sources.

Statutory inquiries have the power under law to order people to provide evidence - and the refusal to do so can see someone end up in prison, although this is still a distant possibility.

An order under the Inquiries Act was made by Sir Charles, with a deadline for this Friday being given to Mr Mercer to comply.

However, he had a deadline of Wednesday to appeal.

A statement from the inquiry said: "The Independent Inquiry relating to Afghanistan has received an application to set aside the section 21 notice from Mr Mercer.

"The application will be put before the chair of the inquiry, The right honourable Lord Justice Haddon-Cave for his consideration, and his decision will be given in due course."

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Writing on social media on Tuesday, Mr Mercer said: "I am aware of tomorrow's deadline from the Afghan Inquiry order that requires me to name the whistleblowers who confided in me.

"I am submitting an application to challenge the order under section 21(4) of the Inquiries Act 2005 seeking to have the Section 21 notice set aside.

"It would not be appropriate to comment further."

Speaking at the inquiry last month, Mr Mercer said he was not naming those who had come to him out of "integrity".

He claims "multiple officers" have told him of allegations of murder and a cover-up in Afghanistan.

Sir Charles said Mr Mercer's decision to "refuse to answer legitimate questions... at a public inquiry" were "disappointing... surprising... and completely unacceptable".

The Afghanistan inquiry was launched in 2022 to investigate allegations of wrongdoing by the British Armed Forces during deliberate detention operations in the country between 2010 and 2013.