The House of Lords has voted to exclude crimes against humanity, genocide, torture, and war crimes from future legal safeguards for UK personnel as part of the Overseas Operations Bill.
Peers, by 333 votes to 228, and a majority of 105, backed an amendment to ensure the most serious of offences are not covered by the proposed legislation, which is aimed at protecting British servicemen and women from vexatious claims.
The Government's Oversea Operations Bill outlines that personnel will not be prosecuted five years after certain offences are alleged to have taken place, unless there are "exceptional" circumstances.
The amendment passed by the House of Lords says crimes against humanity, genocide, torture, and war crimes should not be given such protection.
But ministers said the alterations risked undermining the reassurance they have been trying to give to personnel.
The Government introduced the Overseas Operations Bill with the aim of limiting false and historical allegations against service personnel and veterans in relation to overseas operations.
While not an absolute ban on historic prosecutions, the Government wants the bill to limit false and historical allegations arising from overseas operations by introducing a statutory presumption against prosecution, making it exceptional for personnel to be prosecuted five years or more after an incident.
All overseas operations would continue to be governed by international humanitarian law, including the Geneva Conventions.
However, the Overseas Operations Bill, which has already been through the House of Commons, has faced criticism for not excluding war crimes, crimes against humanity, genocide and torture from its scope, as it did for rape and sexual violence.
Opponents to the proposed legislation have warned the bill in its current form could break Britain's international legal obligations.
Calls for the bill not to cover genocide and torture were led by Labour's former Defence Secretary Lord Robertson, who previously served as NATO Secretary General.
Urging "tactical retreat" by ministers, Lord Robertson said: "For the first time in the history of British law, we would be creating a two-tier justice system where troops acting for us abroad would be treated differently from other civilians in society.
"In addition to that, this bill by saying that there is a presumption against prosecution for the most serious of all crimes, namely genocide, crimes against humanity and torture, it undermines some of the most basic international legal standards for which this nation was renowned."
He added: "I believe this bill is bad for our troops, bad for our British legal system and very bad for our national reputation."
Former diplomat and independent crossbencher Lord Hannay said: "Unamended, this bill would effectively… open the door to a time limitation on the inquiry into and where justified the prosecution of the most heinous of crimes."
The UN High Commissioner for Human Rights said the proposed legislation could shield UK personnel from being held accountable for war crimes.
Defence minister Baroness Goldie, who opposed the amendment to the bill, said: "The Government's decision to only exclude sexual offences does not mean that we will not continue to view with the utmost gravity other offences such as war crimes and torture."
She stated the Armed Forces would continue to operate under international law, adding that the Overseas Operations Bill "neither stops such offences from being investigated nor prosecuted".
The Government also sustained further defeats to the bill, with peers backing changes aimed at preventing personnel facing delayed and repeated investigations into allegations arising from foreign deployments, and removing a planned six-year time limit on troops bringing civil claims against the Ministry of Defence (MOD).
The House of Lords later backed a demand by former service chiefs for greater support to be given to military personnel facing allegations linked to overseas operations, placing a duty of care on the MOD.
The MOD said in a statement: "We continue to assert that the Overseas Operations Bill is a vital piece of legislation, which will address the endless legal cycles and repeated investigations faced by our service personnel in relation to overseas operations.
"None of the proposals will erode the rule of law."
Cover image: Alamy.