The ruling came after a High Court judge attacked the way that ministers had dealt with their case. Mr Justice Sullivan said that the Home Office had failed to follow correct legal procedures and had “deliberately delayed” giving effect to rulings by an immigration adjudication panel.

The judge ordered John Reid, the Home Secretary, to grant the hijackers discrectionary leave to remain, subject to a review every six months. He also made an unprecedented order that the Home Office should pay legal costs on an indemnity basis — the highest level possible — to show his “disquiet and concern”.

Successive home secretaries had failed to grant the nine discretionary leave to enter Britain and allowed them only temporary admission, fearing that to let them live and work in Britain would amount to “a charter for future hijackers”.

Mr Justice Sullivan, sitting in London, said: “It is difficult to conceive of a clearer case of ‘conspicuous unfairness amounting to an abuse of power’. Lest there be any misunderstanding, the issue in this case is not whether the executive should take action to discourage hijacking, but whether the executive should be required to take such action within the law as laid down by Parliament and the courts.”

The nine Afghans were intent on escaping the Taleban when they hijacked a Boeing 727 in Afghanistan on an internal flight from Kabul in February 2000. They forced the crew to fly to Stansted, in Essex. Armed with guns and explosives, they held the plane at the airport for 70 hours surrounded by police and SAS troops before giving themselves up.

The cost to the taxpayer of the hijacking and its aftermath of court hearings and support for the hijackers — who have not been allowed to work — has been unofficially estimated at £10 million.

Jack Straw, the Home Secretary at the time of the hijacking, promised that everyone on the aircraft would be deported “as soon as reasonably practicable”. He said that he was “utterly determined that nobody should consider that there can be any benefit in hijacking”.

But the nine and their families have been living in the London area with restrictions on their movements for years.

In July 2004, an immigration adjudication panel ruled that they could not be sent back to Afghanistan. To remove them would be in breach of Article 3 of the European Convention on Human Rights — not to be subjected to inhuman or degrading treatment. The Government then left them in limbo by failing formally to permit them to enter the country.

In August 2005, Charles Clarke, the third Home Secretary to deal with their case, introduced asylum policy instructions that gave him a new discretion to refuse entry to applicants considered to fall within certain “exclusion criteria”. Last November, he said that the nine came within those criteria, taking into account “the public interest in deterring acts such as hijacking”. He then ruled that it would be inappropriate to grant the nine discretionary leave.

Mr Justice Sullivan said that the Home Office had engaged in “a transparent attempt to find a form of words that would enable the defendant [the Home Secretary] to defy the adjudicators’ decision without having to acknowledge that he was doing so. For a period of nearly 17 months the Home Secretary deliberately delayed giving effect to the adjudicators’ decision in order to give himself time to devise a revised policy which would purportedly justify not implementing the adjudicators’ decision.”

He said that the revised policy of last August was “a paradigm of a minister being given unfettered administrative discretion to depart from a published policy whenever he thinks it appropriate to do so.”

Tony Blair, the Prime Minister, criticised the ruling and said that he hoped the Government would successfully appeal. He said: “We can’t have a situation in which people who hijack a plane we are not able to deport back to their country. It is not an abuse of justice for us to order their deportation. It is an abuse of common sense.”

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