The Northern Ireland Troubles Bill recently began its passage through the UK parliament in London and if passed, could lead to the prosecution of former soldiers who served during "The Troubles".

Three decades of sectarian violence over British rule in Northern Ireland led to the deaths of 3,500 people until a peace deal was signed in 1998.

How to deal with the painful legacy of the conflict remains a thorny issue for both pro-Irish nationalists and unionists, who support Northern Ireland remaining part of the UK.

Just last month, a British soldier was cleared of killing unarmed civilians during the 1972 Bloody Sunday massacre, angering relatives of the victims and political leaders.

But the generals wrote in an open letter to The Times: "Presented as a route to justice and closure, the bill achieves neither.

"It will not bring terrorists to account or heal division in Northern Ireland. Instead, it undermines the confidence of those who volunteer to serve this country at its request and under its authority.

"This lawfare is a direct threat to national security."

The signatories include three former chiefs of the general staff, a former chief of the air staff and former deputy supreme allied commanders of NATO.

They added that members of British special forces were already leaving the service "because they no longer trust the system to stand by them".

The bill also has implications for wherever British forces operate, they said. "Every British soldier must consider not only the enemy in front of them but the lawyer behind," they wrote.

The bill is part of a deal reached between the UK and Irish governments in September to repeal a 2023 law that aimed to end investigations and prosecutions into crimes related to the conflict.

Passed under the previous Conservative government, it notably gave immunity to combatants on both sides, prompting Dublin to take London to the European Court of Human Rights.

The Labour government's new text mainly focuses on reforming the commission looking at the legacy of the Troubles, which families of unionist victims deem to be biased against them.

It also allows the possibility of continuing some ongoing judicial investigations and includes provisions to protect veterans.