[attach id=462136 size="medium"]Shaker Aamer. Photo: Reprieve UK/PA Wire[/attach]

British celebrities and MPs are set to take part in a hunger strike to maintain pressure for the release of the last British prisoner held at Guantanamo Bay.

Authorities announced on September 25 that Shaker Aamer will be freed after more than 13 years in detention without charge.

However, he could not be released immediately because the US administration has to give Congress 30 days’ notice of his release.

Reports have emerged since that the 46-year-old is on hunger strike protesting against alleged abuse at the military prison in Cuba.

Now supporters have launched the Fast For Shaker campaign to show solidarity with Aamer by not eating for 24 hours. Among those taking part are actors Mark Rylance and Maxine Peake, MPs David Davis and Andy Slaughter and the prisoner’s lawyer Clive Stafford Smith. Aamer’s family are also planning to join the campaign.

Organisers said the initiative will start on Thursday and continue until Aamer is released, with participants selecting a day to fast on.

Andy Worthington, co-director of the We Stand With Shaker campaign, said: “After the great news that Shaker Aamer is to be released from Guantanamo, we were all disturbed to discover that he is on a hunger strike and wanted to show solidarity with him and to encourage him to give up his hunger strike.” Aamer, who has a wife and four children living in Battersea, south London, has said he was originally seized by bounty hunters while working as a charity worker in Afghanistan in 2001 shortly after the 9/11 attacks. He was handed over to US forces and in February 2002 he was transferred to Guantanamo Bay and accused of aiding al-Qaeda.

During his time in captivity, his lawyers say he was subjected to torture, with beatings and sleep deprivation, and held in solitary confinement for 360 days. In 2005, he lost half his body weight during a hunger strike.

He was described in US military files obtained by the WikiLeaks website as a “close associate of Osama bin Laden” who fought in the battle of Tora Bora. However, in 2007 the allegations against him were dropped and he was cleared for release.

Despite a formal request by then foreign secretary David Miliband, American authorities refused to allow him to go. A senior US defence official said the decision to return him to the UK had been approved following a “thorough review” of his case and “robust security assurances” from the British government.