In the greatest challenge yet to President Bush’s powers to detain and try terrorist suspects, the Supreme Court agreed to hear an appeal by Osama bin Laden’s driver on whether his trial before a Guantanamo military tribunal is legal. If the court rules against the Bush Administration, the military tribunal process at Guantanamo Bay will be made illegal, giving the White House the challenge of what to do with the 500 detainees held at the Cuban detention facility.

Last summer the Supreme Court, whose decisions must be followed by the US Government, dealt a defeat to President Bush when it ruled, 6-3, that Guantanamo prisoners could challenge their incarceration as “enemy combatants” in US courts. Foreign governments, including Downing Street, have criticised the tribunals as fundamentally unfair because the prisoners have no rights under the Geneva Conventions and limited rights as defendants. All seven Britons held at Guantanamo were sent back to Britain.

The Bush Administration has argued that the Geneva Conventions do not apply to foreign “enemy combatants” and that the military tribunals, where defendants are not allowed to see much of the evidence presented against them, are lawful.

After last year’s Supreme Court ruling, Salim Ahmed Hamdan, accused of being bin Laden’s driver between 1996 and 2001, challenged the legality of his tribunal in a district court in Washington.

In November last year his tribunal, and those of three other detainees, were suspended after a judge ruled that they might be illegal. That decision was unanimously overturned this summer by a three-judge federal appeals court, which included Judge John Roberts, since confirmed as Chief Justice of the Supreme Court. He has said he will not take part in any case on which he ruled as an appeals judge.

Mr Hamdan’s appeal may present an extraordinary baptism of fire for Mr Bush’s latest Supreme Court nominee, Samuel Alito. If confirmed he will be on the court in time for the appeal hearing in March or April.

Mr Alito, a conservative, is expected to be more sympathetic to the White House’s hardline stance on Guantanamo detainees. If the court rules along the same lines as last year, the Bush Administration will be defeated 5-3. But if one more justice backs the Bush policy, the court will deadlock at 4-4. That would mean this summer’s appeals court decision — ruling the tribunals legal — would stand, making the confirmation of Mr Alito even more imperative for Mr Bush.

Another five Guantanamo Bay detainees are to be tried by a special military commission on terror-related charges. Four others are awaiting trial.

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