The controversial Overseas Operations Bill returns to the House of Commons with the government under fire from all directions for how the legislation is shaping up.

Conservative MP Johnny Mercer said he was ‘relieved of his [defence ministerial] responsibilities’ on Tuesday after objecting to a government amendment affecting veterans who served in Northern Ireland.

The bill proposes a five-year limit of criminal prosecutions against veterans but the latest government reversal excludes those who served in Northern Ireland.

Mercer said this exclusion was his ‘red line’ and accused the government of treating those who served in Northern Ireland as ‘second class veterans’.

In a letter to the prime minister, Mercer added: ‘They deserve the protections of the Overseas Operations Bill like everyone else. A policy decision was taken not to include them. I made promises on your behalf that we would not leave them behind and would walk through simultaneous legislation for them. No discernible efforts have been made to do so.’

The government has also acceded to demands from the House of Lords not to amend the Human Rights Act to place a duty to consider derogation from the European Convention on Human Rights in relation to any future overseas operations. It is also being reported that the Ministry of Justice has conceded to an amendment promising to exclude torture, genocide and crimes against humanity from the five-year rule.

But while the government comes under criticism for agreeing to certain amendments, there are many equally critical of them for not going far enough to change the legislation.

The Law Society has called for the complete removal from the bill of the presumption against prosecution for alleged serious offences. Vice president Lubna Shuja said: ‘The government’s amendment to the bill is a step in the right direction, but is damage limitation only and leaves in place a presumption against prosecution for war crimes and other serious offences.

‘This flies in the face of internationally agreed standards and risks setting a dangerous precedent, undermining the UK’s standing internationally and its ability to hold other states to account.’

Meanwhile, there continues to be disquiet about part two of the bill, which imposes a six-year limitation period for personal injury claims against the Ministry of Defence.

The House of Lords last week rejected an amendment to leave out this clause altogether but did vote to exempt veterans – and not civilians – from the time limits.

The Association of Personal Injury Lawyers, which opposes part two of the bill, welcomed the voted-for amendment but warned it does not go far enough and effectively creates a two-tier system by treating civilians differently to service personnel. The government has said it will oppose attempts to amend part two of the bill when the commons debates them this afternoon.