The family and legal team of Guantanamo detainee Omar Deghayes are urging people to write to him inside the top security jail.
Clive Stafford-Smith, the international lawyer who represents Mr Deghayes and more than 40 other inmates, said his client was now "devoid of all hope", and letters from the public would boost his spirits "immeasurably."
Apart from occasional visits from Mr Stafford-Smith, the 36-year-old father from Saltdean has not seen or spoken to anyone from the outside world for almost four years.
He, like other prisoners, has reported severe beatings, mental torture, humiliation and religious abuse at the hands of his guards.
Mr Stafford-Smith said: "He has been in there so long now, in such awful conditions, with no charge brought against him, that he is devoid of all hope.
"He doesn't believe the British Government is going to help him and he believes the Americans want to send him to Libya, where he will be tortured and likely killed.
"Getting letters from the outside from people who are thinking of him would help him immeasurably.
"It makes him so happy to know that people care."
Mr Stafford-Smith said a regular stream of letters would also serve the purpose of letting the Americans know that attention is being paid to what is happening in Guantanamo.
He said: "It is good to remind them as much as possible that people are watching."
Amani Deghayes, Omar's sister, said: "Letters would help Omar's morale a lot.
"The prisoners are often told that no one on the outside cares about them and they have been forgotten about, as a form of psychological torture.
"The whole design of Guantanamo is to get people excluded and isolated from the rest of the world.
"The more people that write the more we can show both Omar and the Americans that people outside are aware of what is going on and support him."
The Justice for Omar campaign got a boost this week when Health Secretary Patricia Hewitt said she would speak to the Attorney General about the detainee's case.
Save Omar campaigners Jackie Chase and Caroline O'Reilly spoke to her following the filming of BBC's Question Time in the Corn Exchange in New Road, Brighton, on Thursday.
The minister said she would speak to the Attorney General, who is leading the negotiations with the Americans, and find out what was happening.
She has promised to give them an update on the situation on Monday.
Letters for Mr Deghayes should be addressed: Omar Deghayes, Prisoner No 727, 160 Camp X-Ray, Washington DC, 20053, USA.
Mr Deghayes is currently in the seventh week of a hunger strike and could die any day.
Due to the urgency of the situation, we are delivering your messages of support for The Argus Justice for Omar campaign to the Home Secretary tomorrow.
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