UK ministers are set to introduce a ban on prosecutions of Northern Ireland veterans under new legislation to be announced next week.

Boris Johnson’s government is finalising plans to block trials linked to the Troubles and, instead, move towards an approach which it will say will echo the “truth and reconciliation” model used in post-Apartheid South Africa.

The move is likely to prove highly controversial at a time when relations between the main political parties in Northern Ireland are already under strain.

The UK government plans to say that its new approach will place an emphasis on reconciling divided communities in the North, while also renewing efforts to retrieve and recover information about fatalities in a bid to offer a sense of closure to the families of victims.

UK ministers have said they believe that prosecutions linked to the Troubles are increasingly unlikely to result in convictions, because any evidence is likely to be inadmissible due to the passage of time.

In 2019 then Tánaiste Simon Coveney said a pledge by UK Prime Minister Boris Johnson’s to make legal changes which could end prosecutions of British army veterans were “very concerning”.

He wrote at the time that the governments and parties had already agreed an approach on legacy and reconciliation in Northern Ireland.

“There is no statute of limitations, no amnesty, for anyone who committed crimes in NI [Northern Ireland],” he wrote.

“The law must apply to all, without exception, to achieve reconciliation.”

On Tuesday, the murder trial of two ex-paratroopers accused of shooting Joe McCann, an IRA commander responsible for the deaths of 15 British soldiers, collapsed after just six days.

A judge in Belfast ruled as inadmissible statements the soldiers – known only as Soldier A and Soldier C – had been compelled to give to a superior officer in the hours after the shooting.

The forthcoming Bill on Northern Ireland legacy issues is expected to introduce a statutory bar on prosecutions related to the Troubles. It will apply across the board in the region – covering former IRA members as well veterans of the UK armed forces.

It is distinguished from an amnesty, which involves the government formally pardoning people. Nor will it apply retrospectively; previous convictions will still stand. An exemption will be carved out for gross human rights violations, such as torture or war crimes, it is understood.

The mechanism will be significantly tougher than that brought forward to protect current and former personnel related to their service abroad, which was set out in the Overseas Operations Act that became law last month.

That legislation, led by the Ministry of Defence, set out a statutory presumption against prosecution once five years has lapsed after an alleged crime committed by a member of personnel on active duty abroad.

It is understood that the precise details of the Northern Ireland legacy Bill, which is being led by the Northern Ireland Office, are still being finalised and only a faint outline may be offered at the Queen’s Speech on Tuesday.

Johnny Mercer, who was recently sacked as Veterans’ Affairs minister, has highlighted that the past two Queen’s Speeches have contained lines promising to take action to protect veterans of Northern Ireland – but the government has so far failed to deliver. He is leading a protest against the ongoing prosecutions with a march on Westminster planned for this Saturday. More than 20,000 people have currently signed up to attend.

Meanwhile, up to a dozen army veterans face a fresh murder investigation into the deaths of civilians in Belfast’s “Bloody Sunday” 50 years ago.

An inquest next week into the Ballymurphy massacre is expected to conclude that 10 people fatally wounded over three days of violence in August 1971 were unlawfully killed.

The coroner Mrs Justice Keegan will then refer her findings to Northern Ireland’s Public Prosecution Service which will consider whether to bring charges against ex-paratroopers, all of them now in their 70s and 80s.