A new deadline has been set for Johnny Mercer to argue why he should not have to hand over the names of those who told him about alleged special forces murders in Afghanistan.

Sir Charles Haddon-Cave, chairman of the Afghanistan Inquiry, gave Mr Mercer until 4pm on April 5 to provide a witness statement containing the names or face a potential prison sentence.

But the deadline was extended while the chairman considers Mr Mercer’s application to challenge the order.

The veterans’ minister has until 4pm on May 8 to make any further submissions or evidence, Sir Charles has ordered.

During Mr Mercer’s evidence to the inquiry last month, the chairman said his decision to “refuse to answer legitimate questions … at a public inquiry” were “disappointing … surprising … and completely unacceptable”.

This came after Mr Mercer repeatedly refused to hand over names of “multiple officers” who told him about allegations of murder and a cover-up, during his time as a backbench MP.

By April 29, counsel to the Inquiry Oliver Glasgow KC will prepare a note setting out “any relevant legal or factual matters… pertinent to the application”, a copy of which will be provided to Mr Mercer and his lawyers, the chairman said.

The MP for Plymouth, Moor View will then have nine days to respond.

Giving his reason for not disclosing the names, he told Mr Glasgow last month: “The one thing you can hold on to is your integrity and I will be doing that with these individuals.”

The inquiry said Mr Mercer was served with a Section 21 notice on March 13, compelling him to hand over the names, which the inquiry has said will be “treated in confidence”.

In the order, the chairman said the consequences of failing to comply without reasonable excuse would be “a criminal offence punishable with imprisonment and/or a fine”.