The government is facing a legal challenge over its refusal to ensure two Isis militants are not executed when they are sent to the US for prosecution.
Elsheikh’s mother is attempting to launch a judicial review of Sajid Javid’s unprecedented decision not to seek assurances that the death penalty would not be used, when he handed over British intelligence.
But the legal action may not stop the pair, who are alleged members of the British terror cell known as “the Beatles”, being transferred from custody in Syria to the US.
“The Americans can do what the Americans want,” a government source told The Independent.
A spokesperson for the US State Department said it would “continue to pursue all diplomatic avenues” but would not confirm whether its plans for Kotey and Elsheikh were affected by the pause in British assistance.
After the home secretary’s letter to the US attorney general was leaked, a solicitor representing Elsheikh’s mother wrote to the home secretary “asking for his immediate undertaking that mutual assistance should not continue to be provided”.
“The letter explained that in the absence of an undertaking, an immediate application would be made to court for an injunction preventing further provision of assistance in light of an unlawful decision by the minister, until such time as a court could determine its legality,” said a statement from solicitors’ firm Birnberg Peirce.
“Mr Elsheikh’s mother had long made clear her wholesale opposition to the actions of Isis. Her request is that the norms of internationally accepted due process form the basis of any trial of accusations concerning her son.”
The Home Office pledged to stop any further assistance to US prosecutors until a court determines whether the legal action will progress, and must formally respond to the mother’s claim within a week.
But British authorities may have already sent over the bulk of material from a four-year counterterror investigation into Kotey and Elsheikh to their American counterparts, who may be able to progress regardless of the challenge.
A Home Office spokesperson confirmed it had agreed to a “short-term pause” in mutual legal assistance because of the mother’s request, but added: “The government remains committed to bringing these people to justice and we are confident we have acted in full accordance of the law and within the government’s longstanding MLA policy.”
Solicitors said their application for judicial review aimed to determine the legality of Mr Javid’s failure to demand assurances that Kotey and Elsheikh would not be subjected to the death penalty.
“The application raises questions of enormous constitutional importance, including the ability of a minister – without reference to parliament – to agree to so complete a departure from a prohibition understood by all to have the status of constitutional certainty and without any public debate,” representatives said.
It called a letter sent by the home secretary to the US attorney general on 22 June a “clear and dramatic departure from the UK’s long standing international and domestic commitment” to oppose the death penalty.
The document, which only became public when it was leaked to the media this week, said Britain “does not currently intend to request, nor actively encourage” the transfer of Kotey and Elsheikh to Britain from Syria, where they are currently being held by the Syrian Democratic Forces (SDF) alongside thousands of other foreign fighters.
“I am of the view that there are strong reasons for not requiring a death penalty assurance in this specific case, so no such assurances will be sought,” Mr Javid added.
“We believe that a successful federal prosecution in the US is more likely to be possible because of differences in your statute book and the restrictions on challenges to the route by which defendants appear in US courts.”
The Howard League for Penal Reform is also examining the possibility of legal action against the government, and MPs of all parties condemned the failure to consult parliament.
Tory grandee Ken Clarke was among the Conservatives condemning the government, saying the UK “must not let its standards slip” in the face of terror.
Ben Emmerson QC, a former United Nations special rapporteur on human rights and counterterrorism, said the decision was “unprincipled, incompetent and almost certainly unlawful”, and Lord Carlile called it “extraordinary”.
Diane Foley, the mother of murdered hostage James Foley, has called for Kotey and Elsheikh to be jailed rather than killed – and their former captive Nicolas Henin told The Independent he did not want them to be given the “satisfaction” of martyrdom.
But Downing Street threw its weight behind the Home Office by saying Theresa May supported its handling of the case.
Ben Wallace, the security minister, argued in the House of Commons that seeking an assurance against the death penalty might “get in the way” of a US trial.
He was jeered for suggesting the alternative was letting Kotey and Elsheikh “roam free”, and used Isis’s horrendous crimes to bat away questions from MPs over why the government had not followed normal policy.
“We are not going to seek assurances because it is our reality that we do not think we have the evidence here to try them in the UK,” he added, confirming they had been stripped of British citizenship.
“At the end of the day, this is about the security of our country and about security being delivered where it can be done.”
Terror experts have cautioned that executing Kotey and Elsheikh would hand Isis a fresh propaganda victory as it seeks to regroup in new “wilayat” (provinces) following territorial losses across Syria and Iraq.
Originally from London, the pair 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.
Surviving captives 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.
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