Shaker Aamer, the last British resident held in Guantanamo Bay, has been brutally beaten on film at least 315 times by guards, it has emerged.

As David Cameron prepared to fly to Washington for talks with Barack Obama seeking his release, it was revealed the father-of-four is routinely assaulted by guards for peaceful protests.

Campaigners said the 46-year-old terror suspect, imprisoned at the notorious military camp without charge or trial for almost 13 years, was subjected to a violent procedure known as a ‘forcible cell extraction’ by teams of riot officers.

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Campaigners claim that Shaker Aamer, pictured, is assaulted on a regular basis by U.S. military guards

Last night they urged the Prime Minister, who will raise Mr Aamer’s plight at the White House tomorrow, to demand video footage showing chilling evidence of his ill-treatment.

The Prime Minister is travelling to the US for his last scheduled encounter with the President before May’s General Election.

He has pledged in a letter to ‘seek further assurances’ from Mr Obama that Mr Aamer – who vehemently denies having close links to Osama bin Laden – has not been the victim of abuse at the controversial naval facility in Cuba.

British officials are attempting to persuade the US that they can deal with any security concerns about his return to London.

Mr Aamer, who the US military believed was a ‘recruiter, financier, and facilitator’ for Al Qaeda, is understood to have agreed to be placed under a strict security regime if he returns to London, including T-Pim control orders, curfews and restrictions on who he can meet and telephone and internet use.

Last night Clive Stafford Smith, of human rights charity Reprieve, which represents the Londoner, said video tapes recorded during the cell extractions would offer proof that baton-wielding guards had beaten his client.

Until now, ministers have been unwilling to ask the US for the images, the existence of which was established in a separate court case of a Syrian detainee on hunger strike at Guantanamo.

Mr Stafford Smith said that following last month’s DEC bombshell US Senate intelligence committee report which exposed the scale of CIA torture of terror suspects, it was vital Mr Cameron raised the issue of abuse.

He said: ‘In the wake of the shocking torture report, the Prime Minister is right to look into the mistreatment of Shaker Aamer at Guantanamo.

‘We will see whether he is told the truth, or shown the 315 videos of Shaker being abused. Shaker continues to be subjected to regular violent assaults simply for peacefully protesting his detention without charge or trial.

‘How in the name of all that is holy can the British governemnt refuse even to ask to see known physical evidence of the on-going abuse of a British resident in US custody?

‘Such a request would doubtless go a long way towards ending some of the mistreatment. I do not understand the British government’s failure in Shaker’s case: how can it be that our closest ally can continue to abuse a British resident and we are powerless to persuade them to stop?’

In declassified phone conversation with his lawyer Mr Aamer, a Saudi citizen who has resident status in the UK, said ‘forced cell extractions’ involved a team of six guards.

For frequent searches, detainees are ordered to lay down on their stomach, put their hands behind their back and cross their legs.

In the event of any resistance, the guards will painfully push pressure points on the body, shackle a captives arms and legs, and strike out to get the prisoner to comply. Critics have dubbed the practice the ‘Gitmo [Guantanamo] Massage.’

Mr Aamer, 46, from Wandsworth in South London, where he has a British wife and four children, has twice been cleared for release from the prison by the Bush administration in 2007 and again by President Obama in 2009.

The US administration has said it is ‘aggressively pursuing the transfer’ of the detention camp’s remaining inmates. The number has plunged to 127 and President Obama has vowed to close Guantanamo before the end of his term in office.

But Mr Aamer’s detention has been extended as US officials insist he must go back to Saudi Arabia where he was born, rather than re-join his family in Britain.

He has repeatedly refused to be dumped in the Middle Eastern emirate, amid serious concerns he would face torture.

Mr Aamer’s lawyers claim the intention is to silence their client - who claims to have witnessed torture in the presence of a British security official.

But a Congressional row in the US could curtail any possibility of release. Republican senators have introduced new legislation to clamp down on President Obama’s ability to transfer terror suspects out of Guantanamo in the wake of the Paris terror attacks.

It would prohibit the transfer of terror suspects considered to be high or medium-risk – which Mr Aamer falls under.

Saudi-born Mr Aamer moved to London almost 20 years ago and married, securing leave to remain in Britain. In 2001, he was detained in Kabul after, his representatives claim, going to Afghanistan to carry out peaceful voluntary work for an Islamic charity.

Prime Minister David Cameron, left, said he would raise Mr Aamer's case with President Barack Obama, right

His supporters claim he was captured by bounty hunters, handed to the US military for $5,000 and then tortured at a secret ‘black site’ prison - effectively a dungeon - at Bagram air force base. He was then sent to Guantanamo Bay in February 2002.

The detention centre was opened in the wake of the September 11 attacks to hold ‘enemy combatants’ in what the US called a war on terror.

Kate Allen, Amnesty International’s UK director, said: ‘David Cameron shouldn’t leave Washington without a cast-iron guarantee over Shaker Aamer’s release from Guantánamo Bay.

‘This terrible farce has gone on for 13 miserable years. We need a date - no more delays, no more excuses.

‘Mr Cameron needs to make it absolutely clear to the US President that Shaker’s release should be a matter of days in coming, not weeks or months.’