The Home Secretary's bid to deport the radical cleric Abu Qatada has suffered a major setback, after Appeal Court judges backed an earlier immigration court ruling that the preacher must not be sent back to Jordan.
Although a Home Office spokesman said efforts to deport Abu Qatada would continue, Labour claimed Theresa May's deportation strategy had been "ripped apart".
The Court of Appeal ruling means the cleric could soon be released from Belmarsh prison.
He is currently being held for allegedly breaching his strict bail conditions, but with no real prospect of his deportation anytime soon, it is unlikely Home Office lawyers will be able to convince the courts to keep him locked up.
In November last year, Special Immigration Appeals Commission (SIAC) judges blocked Abu Qatada's deportation to Jordan.
Siac judges said there was a "real risk" that statements from Qatada's former co-defendants Abu Hawsher and Al-Hamasher, who were allegedly tortured, could be used against him at a retrial, breaching his human rights.
The Court of Appeal has agreed with that assessment.
Unanimously dismissing Mrs May's appeal and upholding Siac's decision, the appeal judges ruled: "Siac was entitled to conclude that there is a real risk that the impugned statements will be admitted in evidence at a retrial and that, in consequence, there is a real risk of a flagrant denial of justice."
Lord Dyson, sitting with Lord Justice Richards and Lord Justice Elias, said the court accepted that Qatada "is regarded as a very dangerous person", but that was not "a relevant consideration" under human rights laws.
A Home Office statement following the Court of Appeals ruling said the department planned to seek leave to appeal.
A spokesman said: "This is not the end of the road and the Government remains determined to deport Abu Qatada. We will consider this judgement carefully and plan to seek leave to appeal.
"In the meantime we continue to work with the Jordanians to address the outstanding legal issues preventing deportation."
Responding to the judgement, Shadow Home Secretary Yvette Cooper said: "This is a serious and disappointing judgement which rips apart Theresa May's strategy for deporting Abu Qatada and contradicts her repeated assurances to Parliament that her approach would get him swiftly onto a plane."