Detainees inside the US camp at Guantánamo Bay are being exposed to increasingly brutal sleep deprivation techniques with doors outside inmates' cells allegedly being slammed by guards up to 300 times a night.

According to Shaker Aamer, the last British resident inside the camp, one guard had told him that he was following orders by making as much noise as possible while detainees – many on hunger strike – tried to sleep.

Aamer, 46, in a letter written on Thursday, said: "He admitted to me: 'It's my orders to keep going up and down all night tonight'. They crashed the doors maybe 250 to 300 times in the night, keeping us awake, and continued until around 9am – then quiet."

One theory is that the escalation in disruptive behaviour is part of the camp's preparation for force-feeding of detainees during Ramadan.

US authorities have claimed that they intend to force-feed only during the night in order to avoid breaking the daytime fast which is the central feature of Ramadan.

However they have yet to say how they will implement night feeding amid concern that the prison may become "a veritable force-feeding factory" during the religious period.

Lawyers for detainees say that dozens of restraint chairs and hundreds of staff might be needed to carry out the force-feeding of 45 inmates in the 10 hours between sunset and sunrise, with each person requiring an hour of feeding time and four hours of total observation time.

Clive Stafford Smith, director of Reprieve, who spent last week inside Guantánamo Bay, said: "It's baffling that the US military is trying so hard to crush the hunger strike, when it could end it tomorrow by transferring cleared prisoners.

"It's especially disgusting that the JTF-GTMO [Joint Task Force Guantánamo] spokesperson calls night-time force-feeding in Ramadan a privilege, not a right."

Aamer, in a letter to Stafford Smith, his lawyer, also explained that he had also been affronted on other religious grounds.

Aamer, whose family live in south London, explained how he had kept his Qur'an in a plastic bag bag for more than three years to protect it from dirt, water and to stop guards from touching it.

However Aamer said that officials had told him that he had to hand back the plastic bag.

"I told them I can't keep my Qur'an without protecting it from MPs [military guards] and other damage, so they must, if they had to, take both the bag and the Qur'an.

"In the end they refused to let me have the bag and I had to give up my Qur'an. So they called the Muslim translator and took the Qur'an from me. That was the end of another day in this terrible place."