British troops facing investigation over alleged historical offences will be granted stronger legal protections, the new Defence Secretary is set to announce.

Penny Mordaunt will propose legislation to ensure veterans and serving personnel are not subjected to repeated investigations on historical operations.

However, the measures will not apply to cases arising in Northern Ireland.

The proposals, subject to a public consultation, include measures to introduce a statutory presumption against prosecution of current or former personnel for alleged offences committed in the course of duty abroad more than 10 years ago.

It will stipulate that such prosecutions are not in the public interest unless there are “exceptional circumstances”, such as if compelling new evidence emerged.

Ms Mordaunt, who is expected to unveil the new measures within days, 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 Cabinet minister is also expected to reaffirm her commitment to derogating from the European Convention on Human Rights (ECHR) before the UK embarks on significant military operations.

In 2016, Theresa May announced that the Government will adopt a presumption that it will take advantage of a right to suspend aspects of the ECHR at times of war.

Mrs May said at the time that the move should end an “industry of vexatious claims” which has seen veterans of Iraq and Afghanistan pursued through the courts over alleged mistreatment of combatants and prisoners over a decade after the supposed events took place.

Separately, Ms Mordaunt is due to address the First Sea Lord’s Sea Power Conference on Wednesday morning.

PA