By Jon Silverman Legal affairs analyst

The ruling by the Special Immigration Appeals Commission that nine men, arrested as terrorist suspects under legislation rushed through parliament, are being held unlawfully is an acute embarrassment to the government - though it almost certainly won't lead to the imminent release of the suspects.

But given that the commission was shown secret intelligence assessments which were the basis for the detentions, and yet still called the arrests " disproportionate", ministers will now face questions about a process which lawyers have criticised as "bizarre, irrational and extraordinary ".

The nine foreign-born men were detained under the Anti-Terrorism, Crime and Security Act, which became law last December as an emergency response to the al-Qaeda attacks of 11 September.

Insufficient evidence

There was not sufficient evidence to charge them with an offence.

Neither could they be deported to their country of origin because of European Convention obligations not to deport to states which practise torture or the death penalty.

The government's compromise was to detain without charge in the UK while stating that the suspects were free to leave the country at any time if they could find a safe haven.

At the heart of the judgment is the principle that it is unlawful to discriminate against someone on the basis of nationality

The Home Secretary said his measure "addresses our essential liberties with calmness but purpose".

That assessment has now been undermined by today's ruling.

At the heart of the commission's judgment is the principle that it is unlawful to discriminate against someone on the basis of nationality.

In other words, a Briton who was suspected of terrorist involvement but against whom there was no compelling evidence capable of being tested in court, could not be imprisoned without charge.

Thus it is wrong that a foreign-born person can be.

The ruling was made by interpreting the European Convention of Human Rights.

Ironically, the government thought it had dealt with this problem by opting out, or derogating, from part of the convention.

'MI5 Setback'

But in the commission's view this was a faulty procedure and the home secretary, David Blunkett, may at some point have to return to parliament if he doesn't wish to amend the act itself.

As well as a blow to ministers, this is also a setback to MI5.

It was information from the security service on which Mr Blunkett and his advisers made their decisions to detain.

Indeed, MI5 had wanted an even wider sweep of suspects and while the service maintains that each one of those behind bars is a potential threat to the UK, its judgment - as in some previous instances where Muslim suspects have been detained in Britain - has been called into question.