Ministers could seize on revelations in The Independent yesterday that police and MI5 now believe there is no link between the two London bomb plots on 7 and 21 July, after scouring all their known contacts and phone calls.
Proof that the bombers acted independently could substantiate claims that so-called "preachers of hate" and Islamist militants in Britain play a central role in fostering home-grown terror cells, without the need for a foreign mastermind.
The men's lawyers, who deny their clients have any links to terrorism in the UK, are furious at the decision to reopen the high-security unit. Gareth Peirce, the lawyer for seven of the 10 detained men, mostly Algerians, said yesterday that the unit was "literally covered in cobwebs" and "unfit for humans".
It was closed by the prison service in the late 1990s after it was condemned by the then Chief Inspector of Prisons, Sir David Ramsbotham, as too draconian.
The first in a long series of court challenges to the men's deportations is due to be launched early this week, amid reports that the best-known detainee, the Jordanian cleric Abu Qatada, could be returned to Jordan as early as this week.
The men's lawyers will accuse the Home Secretary of breaching their basic human rights without any proof that they pose a direct threat to Britain, since both Algeria and Jordan are notorious "torture states".
The Government's written assurances from Jordan that Mr Qatada will not be tortured are "worthless", Ms Peirce said. The cleric was branded a "truly dangerous individual" by judges last year.
But the Home Office told a secret court hearing that it would be unsafe to send Mr Qatada back to Jordan because "he is likely to face persecution or breaches of his human rights" there.
Amnesty International said the European Court of Human Rights had previously ruled against a decision by Sweden to deport a detainee back to Jordan. Sweden ignored the ruling but the man, called Mansi, was ill-treated by the Jordanians and the Swedes were forced to readmit him.
Amnesty's experts have also raised serious doubts about human rights standards in Algeria, where nine of the 10 detainees come from. Ministers are in the last stages of drawing up a written agreement with Algeria that no returnees will be abused or harmed.
However, the human rights group said it had uncovered clear evidence that the Algerian military security police use torture with impunity because judges "routinely overlook" allegations of abuse.
"Any assurances given by Algeria's civil authorities to foreign governments that returnees who are at risk of arrest by the security police will not be subjected to torture must be seriously called into question," Amnesty said.Reuse content