A former security minister has accused Lord Hermer of “treason” over his role in a notorious “witch hunt” against British troops.

Tom Tugendhat said the Attorney General’s position was “completely untenable” as pressure mounts on the Prime Minister to sack his closest Cabinet ally following The Telegraph’s revelations.

Speaking at a Policy Exchange event in London on Wednesday, Mr Tugendhat said Lord Hermer had “prioritised” the interests of Islamic Revolutionary Guard Corps (IRGC) agents after this newspaper revealed his leading role in one of the most “offensive” bogus war crimes cases ever brought against British troops.

“His position is completely untenable. He has prioritised – by choice, if also by ignorance – the interests of agents of the IRGC,” he said.

The MP for Tonbridge said Lord Hermer’s role in the Al-Sweady scandal could amount to a criminal betrayal of the national interest.

He said: “Even if his action was unwitting, his belief that those who pursued prosecution of those we ask to protect us are more worthy of praise than the soldiers who risk their lives, demonstrates a failure of judgment and raises real questions about the advice he offers the Government.

“Those who lie about our troops encourage others to kill them. That’s treason. No minister, no citizen, should praise that.”

Last week, The Telegraph revealed how Lord Hermer, then a barrister in private practice, pressed for compensation for a group of Iraqis who accused British troops of murder and torture despite repeated warnings their claims were “nonsense”.

The claimants said they were innocent civilians captured by British troops at the Battle of Danny Boy in 2004 after becoming caught up in fighting between UK forces and the Iranian-backed Mahdi Army. They also claimed they had witnessed British soldiers execute 20 civilians in cold blood.

But during the £31m Al-Sweady inquiry, Lord Hermer’s clients were exposed in 2014 as members of the same militia that had ambushed the British, and their allegations were found to be “deliberate lies”.

On Sunday, The Telegraph revealed how the now Attorney General denigrated British soldiers after his war crimes case against them was exposed as a lie. In an email to a fellow human rights lawyer on the case, he said she had made a “real difference” to people’s lives, and that this was not something the falsely accused veterans could “ever” say.

Mr Tugendhat, a former British Army intelligence officer who served in Iraq and Afghanistan, said the chief law officer was, at best, naive to the risk of exploitation by an enemy state and should have been disqualified from ministerial office because of his role in the scandal.

“You may have thought that praising the recruiting sergeant of His Majesty’s enemies would make you ineligible to serve in His Majesty’s Government. Apparently not,” he said.

He argued that, in the Danny Boy episode, the IRGC had “exploited our own system to punish soldiers for their courage and deter others from following them”.

On Sunday, Gen Sir Peter Wall, former head of the Army and commander of British forces in Iraq following the 2003 invasion, said that Lord Hermer’s “apparent disdain for soldiers on the front line and their contribution to the nation” meant his position “cannot be tenable”.

Nick Timothy, the shadow justice secretary, wrote to the Prime Minister, urging him to fire Lord Hermer. Lord Hermer has also been reported to the Bar Standards Board, the barristers’ watchdog.

Gen David Petraeus, the coalition forces commander in Iraq in 2007-2008, also intervened on Tuesday, warning that Lord Hermer’s “maximalist” legal approach was undermining British soldiers and risking the UK’s relationship with its allies, including America.

The Battle of Danny Boy, a bloody three-hour engagement in May 2004, saw British troops, ambushed and outnumbered by Mahdi Army fighters armed with rocket-propelled grenades and heavy machine guns, forced to fix bayonets and charge across open ground.

Mr Tugendhat said the soldiers’ bravery that day made what followed all the more unacceptable.

“Soldiers fighting hand-to-hand against Iranian-backed militias in Iraq, being hounded by those same militias under a legal mandate carved out by solicitors paid by the very taxpayers who looked to those soldiers for protection from Iranian aggression, only to see that aggression empowered by the courts while their protectors are prosecuted,” he said.

In his speech, the MP also linked Lord Hermer’s position in Government directly to the British Army’s recruitment crisis.

“The Government asks why they can’t hit recruitment targets for our Armed Forces. They ask why half of our young people say they would never fight for their country. Well, they should start by looking at their Attorney General,” he said.

The Telegraph investigation also uncovered other emails revealing Lord Hermer’s views on the Iraq litigation, including one in which he described witness statements from his claimants as “very powerful”, adding: “These Iraqi cases are a good reminder of why I wanted to be a lawyer.”

Mr Tugendhat said the newspaper’s investigation confirmed what many had “long feared”, that the legal culture surrounding Iraq and Afghanistan was not, “in its most aggressive expressions, a neutral application of principle”.

Instead, he said it amounted to a “deliberate” use of legal process “to pursue a narrow political agenda, at the direct expense of the men and women ordered into battle by the British state”.

He said Britain was no longer a “serious military nation” and that the legal landscape Lord Hermer and his colleagues had helped shape was a key reason why Britain’s military was in such a dire position, and that the Iran conflict had “shown us to be legalistic, ill-equipped and unprepared”.

He said an overzealous application of human rights law had created a “straitjacket” for British troops.

A spokesman for the Attorney General said he had the “greatest respect for the Armed Forces and the sacrifice they have made for our country”.

He added: “Over a 30-year legal career, the Attorney General represented many clients, including British military personnel, such as a soldier killed by IRA terrorists and injured servicemen in the Iraq War.

“He always acted with the highest professional standards, and the suggestion he acted for individuals knowing their claims were false is categorically untrue.”