The group – including comedian Frankie Boyle, presenter Janet Ellis and poet Benjamin Zephaniah as well as several high-profile MPs – are backing a campaign to secure the release of Shaker Aamer in a letter published in a national newspaper.
Aamer, one of just over 100 prisoners left at the notorious detention centre, has been held at the US military prison without charge for 12 years, accused of being a close associate of Osama bin Laden, something he denies.
Originally from Saudi Arabia, he moved to Battersea, London, where he has a wife and four children.
The Prime Minister has already raised the case with the US president and Downing Street said last week the UK was “doing all we can to work with the US to encourage them to reach a decision”.
But in the letter sent on behalf of the We Stand With Shaker campaign the group – which includes Tory former shadow home secretary David Davis, Pink Floyd’s Roger Waters and novelist Gillian Slovo – said: “What the US would like to do with Mr Aamer is irrelevant, as the British Government has a non-negotiable responsibility to secure the return of Mr Aamer, given his status as a legal British resident.
“We can find no reason why, given the special relationship between our two countries, Mr Cameron cannot call President Obama and tell him that Mr Aamer must be returned to the UK as swiftly as possible.
“We urge Mr Cameron to pick up the phone to President Obama, and to bring Shaker Aamer home.”
Aamer was detained in Kabul, Afghanistan, in 2001 after, his representatives claim, he went to the country to carry out voluntary work for an Islamic charity.
It is alleged that he was tortured at the Bagram air force base while being questioned by US forces and in February 2010 it emerged that the Metropolitan Police were investigating allegations of MI5 complicity in his torture.
He has been cleared for release since 2009, but on the condition that he returns to Saudi Arabia rather than the UK.
The 47-year-old’s lawyer, Clive Stafford Smith, claims the reason for his continued detention is a fear he will reveal details of brutality he is alleged to have suffered, as well as what he has witnessed happening to other prisoners.
Other signatories included actor Mark Rylance, comedians Jeremy Hardy and Sara Pascoe, theatre director Nicholas Kent and a host of prominent civil liberties campaigners.
The Vatican is asking the United States to find an “adequate humanitarian solution” for prisoners held at the Guantanamo Bay detention centre. The Vatican secretary of state, Cardinal Pietro Parolin, made the request during a meeting with US secretary of state John Kerry.