What is a special appeals tribunal?

The Special Immigration Appeals Commission (SIAC) was set up by the government in 1998. It came in response to a judgment by the European Court of Human Rights over the case of a Sikh activist who had been held in jail in the UK for six years without trial.

The court ruled this was a breach of his human rights and the government was obliged to establish a tribunal at which decisions to deport on national security grounds taken by the home secretary could be heard by judges and contested.

In the present case, we are talking about David Blunkett's decision that a number of people represent a threat to the UK's national security. Because they would face torture or inhuman treatment if deported to their country of origin, they have been detained indefinitely in the UK.

They are free to leave the UK at any time if they wish - and indeed, two of the original detainees have done so.

What are the rules and regulations governing them?

In principle, SIAC is a court of law. But because it is dealing with national security issues, it frequently does not operate like one - especially the commitment to open and transparent justice.

The press and public is frequently excluded from the hearings.

Witnesses - especially, MI5 officers - give evidence behind screens.

The appellants (they are not called defendants because they have not been charged with an offence) have no automatic right to know what evidence is being adduced against them.

Much of that evidence - which would not be recognised as such by a court of law - consists of telephone intercepts/surveillance etc.

What could be the likely impact of Wednesday's decisions?

They can, and almost certainly will, be taken to appeal to the House of Lords by the appellants.

The Lords could even order SIAC to take a fresh look at the cases (this happened with the first person to appear before SIAC, a Muslim cleric from Oldham whom the home secretary wished to deport).

During hearings this summer, an MI5 terrorism expert said the security service may in some cases use information extracted from tortured prisoners.

That prompted human rights campaigners to claim that evidence used by the Home Office in these cases could have been extracted by torture from detainees in other countries - a claim denied by the government.

So one impact could be on the issue of torture and whether a government which subscribes to the European Convention on Human Rights can rely on the use of torture to extract information which might prevent a terrorist outrage.

But an important caveat is that the government has already derogated (withdrawn) from an article of the European Convention in arresting and detaining these people in the first place.

What legislation was used to detain these people?

They were arrested under the Anti-Terrorism, Crime and Security Act, 2001.

Part 4 of the Act allows the immigration service to detain foreign nationals (only foreign nationals, not UK citizens) suspected of being international terrorists.

It also gives the home secretary power to issue a certificate of deportation.

What do human rights groups have to say on the issue?

There was a concerted campaign when the legislation was first framed saying it was an abuse of human rights.

Campaigners say that if the government believes there is a case that certain people are terrorists, they should be charged and appear in court.

Their arguments also focus on the issue of torture.

It is a crucially important issue for both human rights and the government's security policies.