Preacher Abu Hamza has won his appeal against the Government's attempts to strip him of his British passport, a special tribunal ruled today.
The radical cleric argued that such a move would render him "stateless" as he had already been stripped of his Egyptian citizenship.
Delivering its 12-page ruling today, the Special Immigration Appeals Commission (Siac) allowed his appeal.
In his ruling, Mr Justice Mitting said: "We are satisfied on balance of probabilities that if a deprivation order were to be made, the appellant (Hamza) would be made stateless.
"The conclusions which we have reached in the closed judgment supplement, but do not contradict, that conclusion.
"Accordingly, this appeal is allowed."
Hamza, 52, was jailed for seven years in February 2006 for inciting murder and race hate.
He is in Belmarsh Prison as he challenges attempts to extradite him to the US on terror charges.
That case was delayed by the European Court of Human Rights in Strasbourg in July, which called for further submissions over the length of his sentence and the conditions he would experience if extradited to ADX Florence, a so-called "supermax" prison in Fremont County, Colorado.
Attempts to take his passport away were launched in 2003 but delayed by other legal actions against him.
At a three-day hearing in London last month, Hamza's lawyers argued he has already been stripped of his Egyptian citizenship so cannot have his British passport taken too, as that would render him "stateless".
But the Home Office said there was no documentation to prove he was no longer an Egyptian national and though he was once denied an Egyptian passport, he was later allowed one.
The commission heard Hamza may have had his Egyptian nationality revoked but the country's government would not confirm whether he had or not.
The cleric came to Britain on a student visa and acquired a British passport through marriage.
He was denied an Egyptian passport in 1982 because he had not undertaken military service, the panel heard, but a decree in 1988 allowed him his citizenship back.
But Egyptian law expert Sabah Al-Mukhtar, appearing as a witness for Hamza's legal team, told the commission it was possible he had been stripped of his nationality later on for other reasons.
He said by refusing Hamza a passport the Egyptian government was giving a "de facto" denial of his nationality.
The panel heard that under Egyptian nationality laws, a citizen cannot obtain a foreign nationality without government permission.
If they do, that nationality may not be recognised by the Egyptian government.
And Mr Al-Mukhtar said his interpretation of the law was if an Egyptian obtained a foreign nationality without permission, they would be stripped of their Egyptian citizenship.
He said: "There must be a sanction. That could be one of two things - either to treat the acquired nationality as invalid or to lose the original nationality - otherwise it becomes a meaningless provision."
But the expert admitted some of his report was based on speculation as well as Egyptian law.
James Strachan, for the Home Office, said Mr Al-Mukhtar's interpretation was a "fundamental disagreement" with their own expert's evidence.
He said Hamza had travelled to Egypt using a British passport and had been granted a visa to visit the country.
"None of these events require or mean that he has been stripped of Egyptian nationality," he said.
"The 1988 decree demonstrates conclusively that in fact the appellant was granted permission to obtain British nationality and to retain his Egyptian nationality."
The panel heard decisions of people having their nationality taken from them were usually published in the country's Official Gazette.
Mr Justice Mitting ruled it was unclear whether Hamza was stripped of his Egyptian nationality before or after the then-home secretary David Blunkett gave notice of his intention to strip the radical cleric of his British citizenship on April 4 2003.
But he said the panel heard from experts who "had very good grounds for believing, and did believe, that a decree had been issued, probably unpublished, which effectively stripped the appellant (Hamza) of his (Egyptian) nationality".
Mr Justice Mitting went on: "All that we can be satisfied about, on balance of probabilities, is that a decree has been issued and that its effect is to deprive the appellant of Egyptian nationality.
"It is immaterial that the decree was almost certainly issued after the then secretary of state gave notice of his intention to deprive the appellant of his British citizenship on April 4 2003.
"Because the secretary of state cannot make a deprivation order until his appeal has been determined, Siac must take into account all relevant facts and circumstances, whether they occurred before or after notice was given."
A Downing Street spokeswoman said Prime Minister David Cameron was "disappointed" with the decision but that it would not affect ongoing extradition proceedings.
A Home Office spokeswoman said: "We are extremely disappointed by today's judgment and will be considering it closely.
"British nationality is a privilege and the Home Secretary has the ability to remove it from dual nationals when she believes it to be in the public good.
"Today's ruling will not affect the ongoing extradition proceedings against him."