Guantanamo Bay prisoner Omar Deghayes is likely to remain in legal "limbo" for some time, his MP reported after meeting his American captors.
Des Turner, Brighton Kemptown MP, travelled to Washington to raise the case with officials from the Pentagon and the State Department, the US equivalent of the Foreign Office.
While he said a quick release is not in prospect, he believes the Americans are unlikely to release Mr Deghayes to Libya, where his supporters say his life would be in danger.
Mr Deghayes has been detained without charge at the notorious Camp Delta military prison in Cuba since he was arrested in Pakistan in 2002.
The 35-year-old is a Libyan citizen with refugee status in the UK, who has lived with his family in Brighton since 1987.
Dr Turner said: "The Pentagon were surprisingly forthcoming.
"I think we have got a fairly clear indication there is no immediate prospect of him being sent to Libya and I think the Americans have understood the reservations about Libya."
Dr Turner was told the US military divides Guantanamo Bay detainees into three categories.
A fifth are no longer treated as a threat and arrangements are being made for their release.
Lawyers are preparing for tribunals to try a further 20 per cent for alleged terrorist activities.
Mr Deghayes falls into the remaining 60 per cent, who are still considered a threat but do not currently have a case prepared against them.
In March, fellow British resident prisoner Bisher al-Rawi was freed after MP Ed Davey petitioned for his release.
But Dr Turner was not able to secure such a swift result for Mr Deghayes.
He said the system appears slow, but that does not mean there is no diplomacy going on.
He said: "The British Embassy talks to the Americans a lot.
"Although not a lot seems to be happening publicly, a lot goes on behind the scenes."
He believes a House of Lords judgement later this year may affect the status of detainees who were resident in Britain before their arrest.
Dr Turner took a dossier of articles from The Argus's Justice for Omar campaign to the meeting in Washington last week.
Michael Beard, editor of The Argus, wrote a letter to George Bush to accompany the dossier.
He said: "The Argus newspaper has campaigned for justice for Mr Deghayes and his family.
"He may have charges to answer. If so, he should be dealt with according to the rule of law.
"He may be innocent. If so, his indefinite detention in direct violation of the Geneva Convention is even more unacceptable."
Archbishop Desmond Tutu sent a message of hope to Mr Deghayes's supporters when he visited Sussex this month.
The clergyman and human rights campaigner compared those in the US prison in Cuba to people detained in South Africa during the apartheid era.
Dr Tutu said: "Tell them injustice and oppression won't have the last word - that one day they will be vindicated. In South Africa I opposed detention without trial and I have no reason to change."
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