After the possibility of “barbaric punishment or death” was mooted by a lawyer for the Inspector-General of the Australian Defence Force, Mr Roberts-Smith’s barrister Arthur Moses SC retorted his client might be the one in danger.

Mr Roberts-Smith is “the father of two children, has been accused of war crimes against the Taliban and he wears those allegations like a loaded gun every day”, Mr Moses said.

Mr Roberts-Smith, a former SAS soldier and Victoria Cross recipient, is suing Nine newspapers for defamation over reports alleging he committed war crimes while on deployment in Afghanistan and punched a woman in a Canberra hotel.

Nine will vigorously defend its reporting at an eight-week trial due to start on June 7.

Mr Roberts-Smith has subpoenaed the Australian Defence Force and Australian Federal Police in relation to four Afghan witnesses, the Federal Court was told on Friday.

The four people, from the village of Darwan, are expected to testify remotely from Kabul about an allegation Mr Roberts-Smith kicked an Afghan man named Ali Jan off a small cliff and ordered another officer to shoot him.

But Inspector-General James Gaynor has filed a public interest immunity claim against Mr Roberts-Smith’s request, contending the documents – which may or may not exist – should be kept confidential.

The case is already subject to extensive national security confidentiality measures.

On Friday, lawyers were at pains to say they were speaking only in hypotheticals before the hearing was closed to the public altogether.

Barrister Andrew Berger QC said the immunity claim was necessary to protect people in Afghanistan who had co-operated with the Brereton inquiry into Australian war crimes and to ensure Mr Gaynor could continue to carry out his work as Inspector-General.

Mr Berger argued the mere possibility of Taliban retribution should weigh heavily in favour of the claim.

“The Taliban can and does punish people who are perceived to have acted inconsistently with their ideology and objectives,“ he said.

“Your Honour only has to read almost any book about Afghanistan or the Taliban or look at anything on the internet about the Taliban to see time and time again what a horrifying prospect it is, both in terms of the cruel and barbaric nature of punishment they can mete out and the complete disregard for the rule of law.”

Mr Berger also argued the immunity claim should outweigh concerns about the administration of justice as it was a civil, not criminal, case.

“Liberty is not at stake in these proceedings and nor is the protection of the community,” he said.

Mr Moses suggested the threat of Taliban retribution could equally apply to Mr Roberts-Smith.

“We should just pause for a moment and think what the Taliban may or may not do to someone they think has engaged in such war crimes if they ever got their hands on him or his family,” he said.

He said if the Afghan witnesses had previously put forward a version of events about what happened with Ali Jan, Mr Roberts-Smith was entitled to have it.

“What would stop them from coming to this court to tell an absolute lie or an absolute fanciful story that is at odds with a different version given to different people?” he said.

Keeping relevant information confidential, the barrister argued, would result in the judge left sitting on the bench “like a mushroom”, no closer to the truth.

Mr Moses said a “cancer” had begun to spread in the case when an immunity claim was denied last year over a notice that may have been sent to Mr Roberts-Smith warning him of adverse findings in the Brereton inquiry.

Mr Berger said Mr Gaynor “isn’t happy” about that decision, but the answer was not to “let the cancer spread untreated”.

“Two wrongs certainly don’t make a right,” he said.

“Indeed, where might it stop? What other information might spill out? Will there be a cascading series of subpoenas from the parties … and the public interest is thrown under the bus?”

The immunity claim is being supported by the Australian Federal Police.

Justice Wendy Abraham has reserved her decision.