President Bush's controversial military trial system for terrorist suspects held at Guantanamo Bay was dealt a potentially terminal blow by the US Supreme Court yesterday.

In its third rebuke of the Administration's treatment of prisoners at Guantanamo Bay, the court ruled that the 270 foreign suspects have the right under the US Constitution to challenge their detention in civilian courts on the American mainland.

The 5-4 ruling did not order the military tribunal process to be halted but by giving the detainees - many held without charge for more than six years - the right to be heard by a federal judge, it could trigger a rush to civilian courts that, in practical terms, will leave the question of what to do with men such as Khalid Sheikh Mohammed, the alleged mastermind of 9/11, in the hands of the next president.

Barack Obama, the Democratic nominee, has pledged to close down the facility and opposes the military tribunals. John McCain, his Republican opponent, also wants Guantanamo Bay closed.

Unlike Mr Obama, the Arizona senator supported a law rushed through Congress in 2006 by Mr Bush to resurrect the military tribunal system after the Supreme Court last ruled it unconstitutional.

That law, the Military Commissions Act, was passed when Republicans controlled the House and Senate and was the legislation declared unconstitutional yesterday because it denied the detainees the right of habeas corpus - the ability to ask a court if one is being held illegally.

Democrats are now in the supremacy in both chambers and Mr Bush will be hard pressed to get Congress to circumvent the Supreme Court again.

Speaking from Rome, he said that he did not agree with the decision and would consider new legislation to overcome it. "I strongly agree with those who dissented," he said. “Their dissent was based on serious concerns about US national security."

The head of the New York-based Centre for Constitutional Rights, which represents dozens of prisoners at Guantanamo, welcomed the ruling.

“The Supreme Court has finally brought an end to one of our nation's most egregious injustices," its executive director, Vincent Warren, said. “By granting the writ of habeas corpus, the Supreme Court recognises a rule of law established hundreds of years ago and essential to American jurisprudence since our nation's founding."

Five alleged plotters of the September 11, 2001, attacks, including Mr Mohammed, appeared in a Guantanamo courtroom last week for a pretrial hearing. Prosecutors hope to begin trying them on September 15. The future of those trials have now been thrown into doubt by this latest ruling.

Nearly seven years after Mr Bush set up the tribunals, arguing that the detainees had no rights, not one trial has taken place. A military judge at Guantanamo postponed the trial of Osama bin Laden's former driver, due to start last week, pending yesterday's Supreme Court ruling.

The court's liberal justices were in the majority, with Justice Anthony Kennedy pivotal. Writing for the court, he said: "The laws and Constitution are designed to survive, and remain in force, in extraordinary times."

He said the system that the Administration had put in place after previous Supreme Court rulings to classify them as enemy combatants, and to review their status, was inadequate.

The court's four conservative justices dissented. Antonin Scalia said that America was at war with radical Islamists and that the decision “will make the war harder on us. It will almost certainly cause more Americans to be killed."

Commander Jeffrey Gordon, a Pentagon spokesman, said that he had no immediate information on whether a hearing at Guantanamo for a Canadian charged with killing a US special forces soldier in Afghanistan would go ahead next week. Omar Khadr is one of 19 detainees so far facing the first US military war-crimes trials since the Second World War.

Processing the hundreds of detainees through the US federal court system could take years. Many of the detainees' home countries, including Saudi Arabia, Jordan and Egypt, are opposed to taking them back.

Inside the camp

-775 detainees have been held in Guantanamo, about 420 of whom have been released without charge

-David Hicks, an Australian, is the only one to have been sentenced at Guantanamo after pleading guilty in a deal that allowed him to serve out the remaining nine months of his sentence at home

-The US has reported more than 40 suicide attempts among prisoners since the camp opened, with 23 attempting suicide in one ten-day period in 2003

-In May the Pentagon claimed that 36 former inmates were “confirmed or suspected of having returned to terrorism"

Sources: Times database; BBC

Times Recommends

• New York has lost its edge
• Copenhagen will fail – and quite right too
• More than 17,000 new underwater species found