British troops and veterans will be given stronger legal protections against prosecution, Defence Secretary Penny Mordaunt will announce.
The new law would protect them from investigation over actions on the battlefield abroad after 10 years, except in “exceptional circumstances”.
Ms Mordaunt said it would prevent “repeated or unfair investigations”.
The protections, which will be put to a public consultation, would not apply to alleged offences in Northern Ireland.
On taking office earlier this month, after the sacking of Gavin Williamson, Ms Mordaunt said preventing members of the armed forces from being “pursued unfairly” over claims of wrongdoing would be her “personal priority”.
The new protections apply to actions carried out in the course of duty more than a decade ago.
In these cases, there would be a statutory presumption against prosecution for current or former armed forces personnel.
But in exceptional circumstances, such as where compelling new evidence had emerged, the protections could be set aside.
In a statement before the announcement, Ms Mordaunt said: “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.”
She is also expected to repeat the government’s commitment to take up a right to suspend parts of the European Convention on Human Rights before the UK embarks on military operations.
The Ministry of Defence said the suspension, known as “derogation”, would protect British troops from the kind of “persistent” legal claims that followed operations in Iraq and Afghanistan.
An inquiry into allegations against Iraq war veterans was shut down in 2017 after a lawyer representing many of the complainants was found to have acted dishonestly.
The defence secretary is expected to say that lessons from investigating allegations in Iraq and Afghanistan should also be applied to Northern Ireland, although the presumption against prosecution would not apply.
Six former soldiers who served in Northern Ireland during the Troubles are currently facing prosecution.
The proceedings have been criticised by some Tory MPs, including former Army officer Johnny Mercer, who earlier this month said he would not co-operate with the government until it ended the prosecutions.