Charles Clarke, on his first day at the Home Office after Mr Blunkett’s resignation, refused to bow swiftly to the 8-1 judgment. He said that the men held in Belmarsh prison, southeast London, and Woodhill, Milton Keynes, who took the Government to court would stay in jail with other detainees.

In an overwhelming condemnation of the law introduced after the September 11 attacks in the US, the House of Lords ruled that the human rights of foreign suspects held for up to three years without charge or trial had been breached. The decision paves the way for a huge constitutional clash between the judiciary and Parliament.

It was also a big blow to Tony Blair’s determination to put security at the heart of a general election appeal next year, after the humiliating departure of Mr Blunkett.

The new Home Secretary, anxious to show he will match Mr Blunkett’s toughness on terrorism, brushed aside calls from civil liberties groups for twelve detainees held for three years on suspicion of links with terrorism, to be released or charged. Mr Clarke emphasised that his job was to protect national security.“I will not be revoking the certificates or releasing the detainees, whom I have reason to believe are a significant threat to our security.”

Mr Clarke said in a written ministerial statement that the internment provisions would remain in force until Parliament agreed the future of the law. “It is ultimately for Parliament to decide whether and how we should amend the law.”

Despite his defiance, however, ministers are known to be considering a series of measures to enable foreign terrorist suspects to be brought to trial.

These include allowing phone tap evidence, and introducing offences of associating with wrongdoers or committing acts preparatory to terrorism.

Any attempt to continue to hold suspects without trial will be met with fresh legal challenges, lawyers and civil libertarians said last night.

The law lords have no power to strike down measures contained in the Anti-Terrorism Crime and Security Act 2001 but quashed the government “opt-out” from the European Convention on Human Rights as unjustified.

Lord Hoffman said that the case called into question “the very existence of an ancient liberty of which this country has until now been proud: freedom from arbitrary arrest and detention”.

He added: “The real threat to the life of the nation . . . comes not from terrorism but from laws such as these.”

The nine-judge panel ruled that detention without trial was not justified by the scale of the emergency facing Britain. The measures also discriminated against foreign citizens on grounds of their nationality or immigration status.

Gareth Peirce, the solicitor who represented eight of the detainees, said: “It will provoke an enormous constitutional crisis if the Government fails to act swiftly. The Government has to take steps to withdraw the legislation and release the detainees.”

David Davis, the Shadow Home Secretary, said: “This judgment should not come as a surprise. We warned the Government at the time they passed this legislation that it would be difficult to justify.”

Shami Chakrabarti, the director of the human rights group Liberty, said: “Internment has been a festering sore on our nation’s conscience for nearly three years. By acting as judge, jury and jailer the Government has flouted the very values it claims to defend.

“It must now act and charge or release all those currently held without delay.”

She said that if the Government ignored the law lords, it could spark a constitutional crisis.

The emergency measures were rushed through Parliament within three months of the September 11 attacks in the US. In all, 17 people have been detained and 12 remain in Belmarsh and Broadmoor top-security mental hospital, Berkshire. They took their case to the House of Lords after the Court of Appeal backed Home Office powers to hold them without limit or charge.

The Government opted out of part of the human rights convention on the right to a fair trial in order to bring in the legislation.

Any foreign citizen suspected of links with terrorism can be detained or can choose to be deported, but cannot be deported if it would mean persecution in the homeland.

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