Three Algerian men won an appeal against deportation from Britain on Monday in a blow to the government's efforts to throw out suspected foreign militants it views as a threat to national security.

But confusion surrounded the decision on two of the men because the Court of Appeal said its ruling on them was based on secret evidence which it could not make public.

It referred all three cases back to the Special Immigration Appeals Commission (SIAC), a tribunal which has spent years deliberating over the fate of around 15 Algerians the British government wants to expel.

The government acknowledged the three men -- whom media are only allowed to identify by their initials -- could not be deported for the time being. But it said it hoped SIAC would go on to find they could safely be sent home to Algeria.

The three include one man, U, who the government says had direct ties to al Qaeda leader Osama bin Laden.

It says the 44-year-old was "involved in supporting terrorists" behind a "millennium" bomb plot against Los Angeles airport in 1999-2000 and a foiled plan to attack a Christmas market in Strasbourg, France in 2000.

The Court of Appeal said in a written ruling that, on the "open evidence" available to it, it found SIAC was right to conclude Britain could deport U to Algeria without breaching its international human rights obligations.

But it said its confidence in that conclusion was undermined by other, secret evidence submitted to it.

"We cannot, of course, explain in any detail why we have reached that view. All we can say is that we have been shown closed evidence which is capable of undermining SIAC's overall conclusion," the ruling said.

Gareth Peirce, U's solicitor, said she had no idea what the closed evidence contained.

"It's a complete nightmare of comprehension," she told reporters, attacking the secrecy surrounding the judgment and adding that she would seek bail for her clients.

The three men, all in custody, are among a group of Algerians whom Britain is trying to deport after obtaining case-by-case assurances from the Algerian government that they will be fairly treated on their return.

Britain's interior ministry, the Home Office, said it welcomed the Court of Appeal's endorsement of its approach on seeking assurances.

"It is our belief that it is safe to deport to Algeria on the basis of assurances," it said in a statement. It made no comment on the issue of closed evidence.

"It remains our intention to remove these individuals, whom the Home Secretary considers pose a threat to national security, as soon as we are able to do so."

Human rights campaigners say the men are at risk of torture or other ill-treatment if they are sent back to Algeria, and argue that Britain should either charge or release them.