Supporters of Guantanamo Bay prisoner Omar Deghayes want an MP to fly to Washington to plead his case.
Campaigners from the Save Omar pressure group met Brighton Kemptown MP Des Turner on Saturday.
Mr Deghayes, a Saltdean law student and Libyan national, has been imprisoned without charge in the notorious detention centre since he was arrested in Pakistan in 2002.
His supporters want him to be returned to Britain rather than Libya, where they claim his life would be in danger.
His brother Abubaker said: "I hope we can act quickly enough to make sure Omar is not sent to Libya.
"Libyan officials have already visited him and Guantanamo and said they would kill him like they killed my father.
"I want to thank everyone for speaking out for justice for my brother. We just need the Government to listen."
Representatives of the Church of England, Brighton and Hove Muslim Forum, the Green Party, the Labour Party and Respect met Mr Turner at the Friends Meeting House to discuss how to secure Mr Deghayes' release to Britain.
In March, British prisoner Bisher al-Rawi was released after MP Ed Davey petitioned for his release in Washington.
Mr Turner said he would consider making a similar trip to the US - but said his Parliamentary duties come first.
He told The Argus: "It's something I'll be looking at. It is not easy for me to do - you can't just walk away from Parliament."
He has pledged to hand a dossier of letters from Mr Deghayes's supporters to the Home Office, asking ministers to approve Mr Deghayes's return to Britain.
He said: "We'll be stepping up the pressure on the Home Office in particular to get a decision on Omar's future location.
"It is quite clear it will be very helpful if the Home Office would agree to allow Omar back into the country. It could very well be what triggers his release."
Campaign spokeswoman Louise Purbrick said: "This is the broadest range of people we have brought together in a single room, people spoke on behalf of the Church of England, Brighton and Hove Muslim Forum as well as from Respect, the Green Party and the Labour Party.
"We felt that if we can act together to call for Omar's return we could win through the government bureaucracy."
Cori Crider from Reprieve, a legal charity that represents 37 Guantanamo detainees, stated: "The political tide is turning in the US against Guantanamo. The UK can help them close the place down by bringing back its residents. It has done so for Bisher al-Rawi already. The position that Guantanamo should close but that they have no responsibility to help its residents is untenable."
Hangleton and Knoll council election candidate Maggie Clifford, of the Respect party, said: "Omar should be home in the UK and it is a travesty that he continues to be held in Guantanamo Bay after five years in inhumane circumstances.
"I call on the MP for Omar, Des Turner, to visit Washington and add increased pressure for Omar to be brought home now. I also ask for his family to have access to information on Omar's well-being and contact with him immediately."
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