Government powers to detain foreigners without limit under emergency anti-terror laws threaten the values they were designed to protect, the Law Lords were told yesterday.

Nine men held under the Anti-Terrorism, Crime and Security Act are seeking to overturn a Court of Appeal decision which backed powers to detain them without charge or trial.

Their pleas are being heard by a court made up of nine Law Lords, rather than the usual five, because of the constitutional importance of the legal challenge.

Ben Emmerson QC, representing seven of the detainees, said: "We say in a democracy it is unacceptable to lock up potentially innocent people without trial or without any indication when, if ever, they are going to be released. We say it is doubly unacceptable for a democracy committed to the principles of equality and anti-discrimination to single out foreign nationals when it is not prepared to apply the same measures to its own nationals."

He said no one can doubt the terrorist attacks on Washington and New York on September 11 were a direct assault on the values of democracy.

''There is an inevitable temptation for parliaments and governments to fight fire with fire and set aside legal safeguards which exist within a democratic state,'' he said.

Mr Emmerson said the men had been given no idea when, if ever, they will be released, had never been formally interviewed and there was no prospect they they would ever be put on trial. The justification for this was the continuing threat from terrorism.

The hearings resume today.