Senior MPs of all parties have condemned the decision to allow two murderous British Isis fighters to face the death penalty in the United States – as the government admitted it had also secretly lifted objections in previous cases.

Ministers faced a furious backlash after confirming they had not demanded a “no execution” assurance in return for handing over the jihadis, the remaining members of the “Beatles” group.

The move was branded “abhorrent and shameful”, with warnings the UK would be guilty of “arrant hypocrisy” the next time it urged any other country to abandon the death penalty.

Leading Tories joined calls for the pair – currently held by US-backed Kurdish forces in Syria – to be tried in the UK, or assurances sought before they are sent to America, along with intelligence to help their prosecution.

“It is precisely because of the barbaric nature of the crimes which they committed that we, as a country, have to show we are better than them and what they did,” said Labour’s Hilary Benn.

The controversy sparked confusion in No 10, which first refused to say Theresa May backed the decision not to block the death penalty – only to later make clear she did.

In the Commons, a clearly uncomfortable Ben Wallace, the security minister, sparked anger when he claimed seeking a bar on execution might “get in the way” of justice for Alexanda Kotey and El Shafee Elsheikh.

There were jeers when he accused Labour of being willing to leave the pair “free to roam around the United Kingdom” if a prosecution here failed.

At one point, Mr Wallace said he had “respect” for countries that allowed the death penalty, although it is UK policy to oppose it worldwide.

Faces from the Siege: Eastern Ghouta Show all 10 1 /10 Faces from the Siege: Eastern Ghouta Faces from the Siege: Eastern Ghouta Newly arrived civilians from el-Ghouta packed onto a government refugee bus on the front line outside Damascus Nelofer Pazira Faces from the Siege: Eastern Ghouta A small Syrian refugee girl ponders her future on the bus taking her from the eastern Ghouta front line Nelofer Pazira Faces from the Siege: Eastern Ghouta A refugee woman from el-Ghouta who lost her husband and son in the early bombardment by the Syrian army Nelofer Pazira Faces from the Siege: Eastern Ghouta Civilian refugees less than an hour after crossing the front line from their pulverised homes in el-Ghouta Nelofer Pazira Faces from the Siege: Eastern Ghouta Happy to be seen, anxious to conceal their faces: Syrian men who have crossed the east Ghouta front line waiting to be interviewed by Syrian security officers in a nearby refugee camp Nelofer Pazira Faces from the Siege: Eastern Ghouta 29-year old Ala'a Younis, paralysed after a neck wound in eastern Ghouta sits on his wheelchair beside his father Mohamed at a refugee camp near the front line Nelofer Pazira Faces from the Siege: Eastern Ghouta A wheelchair-bound refugee from el-Ghouta describes how he was forced to live in tunnels along with families and Islamic fighters Nelofer Pazira Faces from the Siege: Eastern Ghouta This young woman lost three members of her family in eastern Ghouta before the end of the siege Nelofer Pazira Faces from the Siege: Eastern Ghouta Sana el-Boukeri in a Syrian refugee camp. She lost her civilian husband and son in the Syrian and Russian bombardment of eastern Ghouta while her other son was wounded fighting in the Syrian government army on the other side of the front line. Nelofer Pazira Faces from the Siege: Eastern Ghouta Both sides of history. Sana el-Boukeri's husband and son were killed in the Ghouta bombing by Syria, her other son wounded in the government army Nelofer Pazira

Significantly, the minister revealed that Britons had been sent abroad in the past with no block on use of the death penalty, agreeing to supply MPs with details “for your summer reading”.

The latest decision was set out last month in a letter sent by Sajid Javid, the home secretary, to the US attorney-general, in consultation with the former foreign secretary Boris Johnson.

Standing in for Mr Javid, who was on the cabinet away-day in Newcastle, Mr Wallace insisted UK anti-terror laws were not strong enough to prosecute the fighters in this country.

Ministers had to “balance” their opposition to the death penalty against their “obligation to the citizens of this country,” MPs were told.

“We are not going to seek assurances because we do not think we have the evidence to try them here in the United Kingdom,” Mr Wallace said.

He denied the fighters were being “extradited” because they were not “UK citizens” – confirming longstanding rumours that the pair, both from London, had been stripped of their citizenship.

But Diane Abbott, Labour’s shadow home secretary, said it was impossible to be a “little bit in favour” of the death penalty, adding: “Either we offer consistent opposition or we don’t”.

She added: “This decision to abandon our principled opposition to the death penalty is both abhorrent and shameful, and I call on ministers even at this late stage to reverse this decision.”

Tom Tugendhat, the Conservative chairman of the foreign affairs committee called for them to be tried in the UK for “betrayal”, saying it was “a crime in itself and should be tried as one”.

“Why have we not asked for an assurance, when it would be perfectly possible to do so?” asked Dominic Grieve, the former Tory attorney general.

Lord Carlile, a former independent reviewer of terrorism legislation, told the BBC that the decision was “extraordinary, a dramatic change of policy by a minister, secretly, without any discussion in parliament”.

“It flies in the face of what has been said repeatedly and recently by the Home Office including by Theresa May when she was home secretary,” he said.

Kotey, 34, and Elsheikh, 29, were caught in January this year as they attempted to flee Syria as the coalition against Isis swept through the country.

Their terrorist cell, nicknamed the Beatles by hostages because of its members' British accents, carried out the beheadings of the US journalists James Foley and Steven Sotloff, the US humanitarian worker Peter Kassig and the British aid workers David Haines and Alan Henning.

The leader of the group, Mohammed Emwazi, who was nicknamed Jihadi John, was killed in Syria in 2015.

Mr Foley’s mother, Diane, said she opposed the death penalty for them, telling the BBC: “I think that would just make them martyrs in their twisted ideology.

“I would like them held accountable by being sent to prison for the rest of their lives.”