The Defence Secretary has claimed “illegal wars” instigated by Labour contributed to the legal “mess” faced by British troops.

Ben Wallace made the remark during heated Commons exchanges with shadow defence secretary John Healey, who warned the Overseas Operations (Service Personnel and Veterans) Bill fails to protect troops from prosecution on historical matters.

Mr Healey added the Government is bringing in a “legal presumption against prosecution for torture, war crimes, for crimes against humanity”.

He told the Commons: “This is the Government of Great Britain saying sexual crimes are so serious they’ll be excluded from this presumption, but placing crimes outlawed by the Geneva Convention on a less serious (level) and downgrading our unequivocal commitment for upholding international law that we in Britain ourselves after the Second World War helped to establish.”

His comments were branded “embarrassing” by veterans minister Johnny Mercer sitting on the frontbench.

Some of the veterans I’ve talked to about this Bill reckon it’s more about protecting the MoD than it is about protecting troops.

Mr Wallace then intervened, stating: “What is appalling is the straw man being put up time and time again by a Labour Party half-funded by these ambulance-chasing lawyers that is going to damage our reputation. No apology of the money they took from a number of them, no apology whatsoever…

“Much of the mess we are having to come and clean up today is because of your illegal wars, your events in the past … and to put up straw men and make wild allegations that are wholly inaccurate and disputed by much more learned people than him, I think it a dis-service to our troops and is all about making an excuse for not supporting this Bill.”

Afghanistan and Iraq were the major military campaigns in which Tony Blair sent British troops into combat.

The latter proved particularly controversial, especially in relation to the level of threat actually posed by Iraq’s weapons programme.

The Government believes the new legislation will ensure service personnel will be protected from “vexatious claims and endless investigations”.

It seeks 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.

To override the presumption, the consent of the Attorney General will be required, and the prosecutor must weigh up the “adverse impact of overseas operations on service personnel” and, where there has been no compelling new evidence, the public interest in cases coming to a “timely conclusion”.

But campaigners and some senior military figures have warned that the legislation will create a presumption against prosecution of torture and other serious crimes, except rape and sexual violence.

Opening the second reading debate, Mr Wallace rejected claims that the Bill could decriminalise torture and murder.

He told the Commons: “We’ve been told that this Bill is controversial. Some have gone as far to have said it decriminalises torture or prevents veterans from receiving compensation.

“Both allegations are untrue. I have to question if those making those points have actually read the Bill in full.”

He continued: “It is our intention should new or compelling evidence be brought forward to prosecute for those offences. It is not decriminalising torture, it is not decriminalising murder in any way at all.”

Mr Wallace added: “We want in the future the ability if necessary to allow soldiers to focus on the danger and job in hand when in operations, not on whether they will have a lawsuit slapped on them when they get home.”

But Mr Healey suggested the Bill is more about protecting the Ministry of Defence (MoD) than protecting British troops.

He also said the Bill denies troops who serve overseas the same employer liability rights as the UK civilians they defend, adding Labour wants to make changes to the proposals.

Mr Healey told the Commons: “Over the last 15 years, there have been 25 cases brought by injured British troops against the MoD for every one case brought by alleged victims against our troops.

“So, you can see why some of the veterans I’ve talked to about this Bill reckon it’s more about protecting the MoD than it is about protecting troops.”

He went on: “This legislation will have no impact on any past or any continuing cases … it offers no hope and no help of faster resolution either for troops or alleged victims who may still be involved in long-running litigation or in repeat investigations.”

MPs later approved the Bill at second reading by 331 votes to 77, majority 254.

The division list showed 18 Labour backbenchers rebelled to oppose the legislation, including former leader Jeremy Corbyn, former shadow chancellor John McDonnell and former leadership hopeful Rebecca Long-Bailey.

The Bill will undergo further scrutiny at a later date.