The UK “must not let its standards slip” in the face of terror, Tory grandee Ken Clarke has said amid uproar over the government’s decision not to stop two Isis fighters being given the death penalty in America.

The home secretary broke a decades-long policy of refusing to aid investigations that could result in capital punishment by sharing evidence against alleged “Beatles” Alexanda Kotey and El Shafee Elsheikh.

Currently imprisoned by the Syrian Democratic Forces, they are to be transferred to the US after months of diplomatic wrangling over which country would take responsibility for their prosecution.

In a letter to the US Attorney General, Sajid Javid insisted that the case does not affect the UK’s opposition to the death penalty, but did not seek the normal assurances that it would not be used.

The prime minister was “aware” of the decision but ministers did not seek parliamentary approval and it only became public when the document was leaked to the media.

In a heated debate in the House of Commons, the government was accused of “hypocrisy” as it outwardly continues global opposition to the death penalty.

Mr Clarke, the former home secretary and current chair of the All-Party Parliamentary Group on Extraordinary Rendition, said he could not remember any other cases where assurances against capital punishment had not been sought.

“We should have nothing to do with cases of this kind unless we have assurances that people aren’t subject to the death penalty,” he told The Independent.

Isis 'Beatles' militants captured in Syria: 'It is too late for a fair trial'

“The reputation of this country depends on upholding the highest standards of human rights and individual liberty, and things like torture, rendition and the death penalty should not be part of our tough and effective intelligence services.”

Mr Clarke said that although some members of the public may support capital punishment for Isis fighters, “we can’t slip into that – we mustn’t allow fear to cause us to abandon standards of freedom, liberty and human rights on which this country stands”.

“We must make sure we don’t let our standards slip,” he added.

The government previously bypassed parliamentary approval to launch drone strikes targeting British Isis militants in Syria, announcing them when they had already been carried out and refusing to release the legal advice said to have legitimised the bombing.

The chair of the All-Party Parliamentary Group on drones found last week that ministers’ arguments were “weak and inconsistent”.

Professor Michael Clarke said the government knew that MPs would be unlikely to object to the move because they could not be seen to support Isis fighters.

“Because they were bad guys we said ‘it doesn’t matter’ ... but the principles being compromised are very important,” he told The Independent. “If you’re fighting terrorism you’ve got to be unambiguously lawful in what you do.”

The security minister, Ben Wallace, used Isis’ horrendous crimes to bat away questions from MPs over why the government had not followed normal policy for Kotey and Elsheikh.

“The crimes that we are talking about include the videoed beheading of dozens of innocent people by one of the most abhorrent organisations walking this earth,” he told the House of Commons, accusing critical MPs of wanting them to “roam free”.

But Dominic Grieve QC, the former attorney general who chairs the Intelligence and Security Committee, said it would have been “perfectly proper” to demand guarantees the two men would not be given the death penalty before sharing evidence with the US and warned: “This is going to continue to haunt the government.”

Timeline: The emergence of Isis Show all 40 1 /40 Timeline: The emergence of Isis Timeline: The emergence of Isis 2000 Abu Musab al-Zarqawi (pictured here) forms an al-Qaeda splinter group in Iraq, al-Qa’eda in Iraq. Its brutality from the beginning alienates Iraqis and many al-Qaeda leaders. Timeline: The emergence of Isis 2006 Al-Zarqawi is killed in a U.S. strike. Al-Zarqawi’s successor, Abu Ayyub al-Masri, announces the creation of the Islamic State in Iraq (ISI). Reuters Timeline: The emergence of Isis 2009 Still al-Qaeda-linked ISI claims responsibility for suicide bombings that killed 155 in Baghdad, as well as attacks in August and October killing 240, as President Obama announces troop withdrawal from Iraq in March. Getty Images Timeline: The emergence of Isis 2010 Abu Bakr al-Baghdadi becomes head of ISI, at lowest ebb of Islamist militancy in Iraq, which sees last U.S. combat brigade depart. Timeline: The emergence of Isis 2012 In Syria, protests (pictured here starting in Daree) have morphed into what president Assad labelled a “real war” with emergence of a coalition of forces opposed to Assad’s regime. Syria group Jabhat al-Nusra are among rebel groups who refuse to join, denouncing it as a “conspiracy”. Bombings targeting Shia areas, killing more than 500 people, spark fears of new sectarian conflict. Sunni Muslims stage protests across country against what they see as increasingly marginalisation by Shia-led government. AP Timeline: The emergence of Isis 2013 Al-Baghdadi renames ISI as the Islamic State in Iraq and Syria, or Isis, as the group absorbs Syrian al-Nusra, gaining a foothold in Syria. In response, al-Qaeda chief Ayman al-Zawahiri (Bin Laden’s successor) concerned about Isis’ expansion orders that Isis be dissolved and ISI operations should be confined to Iraq. This order is rejected by al-Baghdadi. AFP Timeline: The emergence of Isis 2014 - January Isis fighters capture the Iraqi cities of Fallujah and Ramadi, giving them base to launch slew of attacks further south. AP Timeline: The emergence of Isis 2014 - June Isis declares itself the Caliphate, calling itself Islamic State (IS). The group captures Mosul, Iraq’s second largest city; Tal Afar, just 93 miles from Syrian border; and the central Iraqi city of Tikrit. These advances sent shockwaves around the world. Timeline: The emergence of Isis 2014 - June Around the same time Isis releases a video calling for western Muslims to join the Caliphate and fight, prompting new evaluations of extremists groups social media understanding. Timeline: The emergence of Isis 2014 - June Isis take Baiji oil fields in Iraq - giving them access to huge amounts of possible revenue. EPA Timeline: The emergence of Isis 2014 - August James Foley is executed by the group as concerns grow for second American prisoner, fellow reporter Steven Sotloff. AP Timeline: The emergence of Isis 2014 - August Obama authorises U.S. airstrikes in Iraq, helping to stall Isis’ along with action by Kurdish forces following the deaths of hundreds of Yazidi people on Mount Sinjar. Timeline: The emergence of Isis 2014 - September Isis release video showing Steven Sotloff’s murder prompting Western speculation his executioner is same man who killed Mr Foley. EPA Timeline: The emergence of Isis 2014 - September Obama tells us that America “will hunt down terrorists who threaten our country” EPA Timeline: The emergence of Isis 2014 - September Isis release a video appearing to show David Haines, who was captured by militants in Syria in 2013, wearing an orange jumpsuit and kneeling in the desert while he reads a pre-prepared script. It later shows what appears to be the aid worker's body. Rex Timeline: The emergence of Isis 2014 - September Peshmerga fighters scrabble to hold positions in the Diyala province (a gateway to Baghdad) as Isis fighters continue to advance on Iraqi capital. AFP Timeline: The emergence of Isis 2014 - October Aid worker Alan Henning is killed. Self-imposed media blackout refuses to show images of him in final moments, instead focuses upon humanitarian care. AP Timeline: The emergence of Isis 2014 - October Isis raise their flag in Kobani, which had been strongly defended by Kurdish troops. The victory goes against hopeful western analysis Isis had overextended itself, while alienating much of the Muslim population through the murder of Henning. Victory causes fresh waves of Kurdish refugees arriving in Turkey. Timeline: The emergence of Isis 2014 - November American hostage, who embarced values of Islam, Peter Kassig and 14 Syrian soldiers are shown meeting the same fate as other captives. But intelligence agencies will be poring over the apparently significant discrepancies between this and previous films. Seramedig.org.uk Timeline: The emergence of Isis 2015 - February Isis has released a video revealing the murder by burning to death of a Jordanian pilot held by the group since the end of December 2014. Reuters Timeline: The emergence of Isis 2015 - February Isis militants have released videos which appear to show the beheading of Japanese hostages Haruna Yukawa and Kenji Goto. Timeline: The emergence of Isis 2015 - February American aid worker, Kayla Mueller was the last American hostage known to be held by Isis. She died, according to her captors, in an airstrike by the Jordanian air force on the city of Raqqa in Syria, though US authorities disputed this. AP Timeline: The emergence of Isis 2015 - February Isis militants have posted a gruesome video online in which they force 21 Egyptian Coptic Christian hostages to kneel on a beach in Libya before beheading them. Egypt vowed to avenge the beheading and launched air strikes on Isis positions. AP Timeline: The emergence of Isis 2015 - February The British Isis militant suspected of appearing in videos showing the beheading of Western hostages has been named in reports as Mohammed Emwazi from London. Rex Features Timeline: The emergence of Isis 2015 - March Isis triple suicide attack has killed more than 100 worshippers and hundreds of others were injured after the group members targeted two mosques in the Yemeni capital of Sanaa. AP Timeline: The emergence of Isis 2015 - April Iraqi forces have claimed victory over Isis in battle for Tikrit and raised the flag in the city. EPA/STR Timeline: The emergence of Isis 2015 - April Isis has claimed responsibility for a suicide bomb attack in Afghanistan that killed at least 35 people queuing to collect their wages and injured 100 more. EPA Timeline: The emergence of Isis 2015 - April Isis’ media arm released a 29-minute video purporting to show militants executing Ethiopian Christians captives. The footage bore the extremist group’s al-Furqan media logo and showed the destruction of churches and desecration of religious symbols. A masked fighter made a statement threatening Christians who did not convert to Islam or pay a special tax. Timeline: The emergence of Isis 2015 - May Abu Bakr al-Baghdadi, the leader of Isis has been "incapacitated" by a spinal injuries sustained in a US air strike in Iraq. He is being treated in a hideout by two doctors from Isis’ stronghold of Mosul who are said to be "strong ideological supporters of the group". Timeline: The emergence of Isis 2015 - May Isis has also claimed responsibility for killing 300 of Yazidi captives, including women, children and elderly people in Iraq AP Timeline: The emergence of Isis 2015 - May Isis attack on Prophet Mohamed cartoon contest in Texas was its first action on US soil. Two gunmen were shot and killed after launching the attack at the exhibition. Elton Simpson and Nadir Soofi have been named as the attackers at the Curtis Culwell Centre arena in Garland. Timeline: The emergence of Isis 2015 - May Isis’s deputy leader, Abu Alaa Afri, a former physics teacher who was thought to have taken charge of the deadly terrorist group, has been killed in a US-led coalition airstrike. Timeline: The emergence of Isis 2015 - May US special forces have killed a senior Isis leader named as Abu Sayyaf in an operation aiming to capture him and his wife in Syria. Getty Images Timeline: The emergence of Isis 2015 - May Iran-backed militias are sent to Ramadi by the Iraqi government to fight Isis militants who completed their capture of the city. Government soldiers and civilians were reportedly massacred by extremists as they took control and the army fled. Charred bodies were left littering the city streets as troops clung on to trucks speeding away from the city. Ramadi is the latest government stronghold to fall to the so-called Islamic State, despite air strikes by a US-led international coalition aiming to stop its advance in Iraq and Syria. AFP Timeline: The emergence of Isis 2015 - May Isis rounded up civilians trapped in Palmyra and forced them to watch 20 people being executed in the historic city’s ancient amphitheatre. The Unesco World Heritage site was overrun by militants, threatening the future of 2,000 year-old monuments and ruins. Thousands of Palmyra’s residents fled but many are still living within the city walls, while the UN human rights office in Geneva said it had received reports of Syrian government forces preventing people from leaving until they retreated from the city. Getty Timeline: The emergence of Isis 2015 - May A group of Isis-affiliated fighters have captured a key airport in central Libya. The militants took control of the al-Qardabiya airbase in Sirte after a local militia tasked with defending the facility withdrew from their positions. Affiliates of Isis, already control large parts of Sirte, the birthplace of former Libyan leader Muammar Gaddafi and a former stronghold of his supporters. Timeline: The emergence of Isis 2015 - June The US Air Force has destroyed an Isis stronghold after an extremist let slip their location on social media. According the Air Force Times, General Herbert "Hawk" Carlisle, commander of Air Combat Command, said that Airmen at Hulburt Field, Florida, used images shared by jihadists to track the location of their headquarters before destroying it in an airstrike. Reuters Timeline: The emergence of Isis 2015 - June Kurdish forces captured a key military base in a significant victory in Raqqa as well as town of Tell Abyad. YPG fighters, backed by US-led airstrikes and other rebels, consolidated their gains, when they seized the key town on the Syria-Turkey border. They are now just 30 miles to the north of Raqqa and have cut off a major supply route deep inside Isis-held territory. Ahmet Silk/Getty Timeline: The emergence of Isis 2015 - June Isis has released gruesome footage claiming to show the murder of more than a dozen men by drowning, decapitation and using a rocket-propelled grenade as it seeks to boost morale among its fanatical supporters. Timeline: The emergence of Isis 2015 - June Isis has begun carrying out its threat to destroy structures in the ancient Syrian city of Palmyra, blowing up at least two monuments at the Unesco-protected site as Syrian government troops made advances on the Islamist’s positions. AFP

Conservative MP Andrew Mitchell pointed out that: “On human rights, we cannot distinguish between good and bad people.”

Diane Abbott, the shadow home secretary, cited calls from the mother of murdered hostage James Foley for a fair trial and another captive who survived told The Independent he did not want to see Kotey and Elsheikh be given the “satisfaction” of execution.

But Mr Wallace refused to reverse the decision and insisted that the US was the “most appropriate jurisdiction” for the pair to be put on trial.

“We are not going to seek of assurances because it is our reality that we do not think we have the evidence here to try them in the UK,” he added.

“At the end of the day this is about the security of our country and about security being delivered where it can be done.”

Mr Clarke said that values had wavered since the 9/11 attacks and rise of jihadi threats, when the UK allowed a “serious lapse in our normal standards” with involvement in extraordinary rendition to Libya and other countries where people faced torture.

“The government continues to make all the right protestations ... but that does not explain why we engaged in it so extensively,” he added, calling for a promised Detainee Inquiry to be reconstituted.

“Something needs to be done to find out exactly what went wrong and to make sure in future it never happens again.”

Mr Clarke said the Intelligence and Security Committee had been “effectively stopped” from investigating post-September 11 cases and that parliamentary scrutiny was being bypassed once again.

Mohammed Emwazi, known as Jihadi John, is among the British Isis fighters killed in drone strikes without parliamentary approval

Mr Wallace insisted that the UK shared intelligence on the basis that Kotey and Elsheikh would not be sent to the Guantanamo Bay detention camp without trial.

Originally from London, both militants were declared “specially designated global terrorists” by the US State Department ahead of their capture in January, with official documents naming them as members of the “The Beatles” and saying the cell had beheaded more than 27 hostages and tortured many more.

Hostages have told of their brutality, which included torture, waterboarding, electric shocks, mock executions, and crucifixions.

Executioner Mohammed Emwazi, who became known as “Jihadi John”, was killed in a drone strike, while the remaining “Beatle” Aine Davis is imprisoned in Turkey.

Kotey and Elsheikh are among the Isis fighters stripped of British citizenship for the “public good” – a power being increasingly used by the government to stop them returning home after the terrorist group was driven out of territories across Syria and Iraq.

The government’s 2018 Transparency Report on Disruptive and Investigatory Powers, which was released on Monday, showed that 104 people were deprived of British citizenship in 2017 – up from just 14 the year before.

Security services have also withdrawn passports from terror suspects to stop them travelling abroad and excluded 26 people from Britain on national security grounds in the year.

A further nine terror suspects were put on “no fly” lists meaning they cannot return to the UK without notifying authorities under set conditions, and eight are currently subject to restrictions under Terrorism Prevention and Investigation Measures.

The Home Office said there were “a range of tools in our toolbox” to disrupt people who pose a security risk, even if they cannot be prosecuted or deported.