Members of the Armed Forces are to be protected from prosecution for historical offences under plans to be unveiled by the new defence secretary - but not if the alleged offences took place in Northern Ireland.

Penny Mordaunt is to put forward legislation designed to ensure service personnel and veterans are not subjected to repeated investigations on historical operations, many years after the events in question.

The proposals include introducing a statutory presumption against prosecution for current or former personnel for alleged offences committed in the course of duty abroad more than 10 years ago.

The presumption, which will be subject to a short public consultation, will stipulate that prosecutions in such circumstances are not to be considered to be in the public interest, except in “exceptional circumstances”.

Compelling new evidence would have to be presented to reopen old cases.

However, the presumption against prosecution will not apply to legacy cases arising in Northern Ireland. Sources suggested that the political tensions in the province had made the issue too difficult to resolve.

As many as 200 British former military personnel are understood to be under official investigation for alleged offences, including murder, which took place during the Troubles, some of them almost fifty years ago.

The presumption against prosecution will not apply to legacy cases arising in Northern Ireland

While veterans groups will welcome the announcement, Ms Mordaunt will come under pressure to find a solution for soldiers who served in Northern Ireland.

The Ministry of Defence said that Ms Mordaunt was looking to apply "lessons learned from historical allegations arising from Iraq and Afghanistan to Northern Ireland legacy cases." The Northern Ireland Office is engaged in a separate consultation over legacy cases, but has previously ruled out an amnesty for troops.

Ms Mordaunt said: “We all owe a huge debt of gratitude to our Armed Forces who put their lives on the line to protect our freedom and security.

“It is high time that we change the system and provide the right legal protections to make sure the decisions our service personnel take in the battlefield will not lead to repeated or unfair investigations down the line."

The defence secretary will announce the new package of measures via a Written Ministerial Statement in the House of Commons in the coming days.

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Johnny Mercer, Conservative MP and former army captain, who has campaigned for some sort of amnesty for troops, welcomed the move.

He told The Telegraph: “I’m delighted with what the Secretary of State has said.

“I will be examining the proposals closely. I am confident that no Government which wants to stay in office will fail to act against this ridiculous process which has destroyed the lives of some of our finest people, whilst lining the pockets of some of our worst.

“Let’s work with the MoD to finally end this charade, and find a way of extending any legislation to ensure that no veteran - wherever they served - is subject to a process which is clearly unfair to all sides”.

In one of her first actions since taking over from Gavin Williamson as defence secretary, Ms Mordaunt will on Wednesday also reaffirm her commitment to derogating from the European Convention on Human Rights (ECHR) where appropriate, before significant military operations are launched.

First announced in October 2016, derogation will protect British troops serving in future conflicts from the kind of persistent legal claims that have followed operations in Iraq and Afghanistan.

Legal arguments that rest solely on ECHR being used to bring claims against the Armed Forces will no longer be allowed, but Britain’s service personnel will still be subject to the rule of the law.

The Government closed down Iraq Historical Investigations Team in 2017 after it became clear that a number of claims being made against soldiers were found not to be credible and that unscrupulous law firms were bringing forward a large number of claims.

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