Since the camp was established on the US naval base on Cuba, prisoners have protested both their treatment and incarceration by launching hunger strikes. Under the administration of Barack Obama, who vowed to close the prison, military guards force-fed prisoners before their weight dropped dramatically.

Yet lawyers say under a new approach adopted by the Trump administration, prisoners on hunger strike are being allowed to physically deteriorate considerably further, as prison authorities engage in a game of “chicken” with the inmates.

“Under the new approach, nourishment will not be given until he is at death’ door, or at risk of organ failure,” David Remes, a Washington-based lawyer who represents Abdul al Salam al Hilal, one of five prisoners on hunger strike, told The Independent. “Under Trump, the warden has reverted to the Bush-era approach to prisoners on hunger strike.”

Reprieve, a London-based campaign group that represents several prisoners, has asked people to people to carry out fasts in support of protesting prisoners, including Khalid Qasim and Ahmed Rabbani, who have gone without food since September 20.

Among those who have taken up the challenge are Pink Floyd co-founder Roger Waters, comedian Sara Pascoe, actor David Morrissey, director and actor Mark Rylance, Labour politician Tom Watson and French-born actress Caroline Lagerfelt.

Waters performed his fast over the weekend. He wrote on Facebook: “Ahmed Rabbani and Khalid Qassim have been in Guantanamo for 15 years.

USA: 'Close Guantanamo' - Protests hit the White House, Washington D.C.

"Neither man has been charged. There is no evidence either man has committed a crime.”

He added: “They have been on hunger strike since 2013 - the only way they have to protest their innocence and affirm their humanity.”

At the height of the so-called war on terror, the prison camp established by George Bush held as many as 780 prisoners - many of them swept up from the battlefields of Afghanistan and Iraq and large numbers of them obtained as a result of paying bounty money. The prison and the military hearings to deal with the images were intentionally set up at the base, as the Bush administration argued it was outside the jurisdiction of the US legal system.

There are currently 41 prisoners held there, each costing US taxpayers $10m a year to incarcerate, as opposed to $78,000 in a federal maximum security prison in the US, according to the group Human Rights First. Only one has been sent to the US for trial in the US courts.

Inside Guantanamo: the diary of Binyam Mohamed Show all 2 1 /2 Inside Guantanamo: the diary of Binyam Mohamed Inside Guantanamo: the diary of Binyam Mohamed Binyam Mohamed claims the US took him to Morocco to be tortured PA Inside Guantanamo: the diary of Binyam Mohamed A cell block which has been converted into a classroom within the "Camp Six" detention facility at U.S. Naval Station Guantanamo Bay Reuters

Of the 41 prisoners, 15 are considered “high value” and include Khalid Sheikh Mohammed, the alleged plotter of the 9/11 attacks.

The five men currently on hunger strike are among a group of 26 men the US is holding for indefinite detention without charge or trial.

“It’s astonishing to me that, 15 years after Guantanamo opened, people are still held there without charge or trial - conditions which some of our clients have chosen to protest peacefully with a hunger strike,” said Shelby Sullivan Bennis, a lawyer at Reprieve.

“Now, under the Trump Administration, we are seeing a brutal attempt to break their strike, and prisoners are being denied basic medical care.”

She added: “Hundreds of people around the world are striking with them to help bring attention to this latest crackdown - and to show Donald Trump that he must either charge my clients, or release them.”

Lawyers for those on hunger strike are increasingly concerned about the health of their clients. Mr Remes said Mr Hilal’s weight had dropped from 165lbs to 110lbs and that he has been coughing up blood.

He said Mr Hilal, who had been held for more than 15 years without being charged, had launched his protest after he was refused permission for a second phone call a month to his family in Yemen.

Reprieve said Mr Rabbani’s weight was down to just 95lbs and that he had long suffered from internal bleeding.

Clive Stafford Smith, the founder of Reprieve and who is also fasting, saying Mr Rabbani had told him: “I don’t want to die, but after four years of peaceful protest I am hardly going to stop because they tell me to. I will definitely stop when President Trump frees the prisoners who have been cleared, and allows everyone else a fair trial.”

Major Ben Sakrisson, a Pentagon spokesman, denied there had been a change in policy and claimed all prisoners were “treated humanely and in compliance with US and international law”.

“There has not been a change in policy, existing policy is just being reinforced with our personnel,” he said.