Campaigners battling to force the release of a Guantanamo Bay inmate held for 11 years without trial are to go on hunger strike in Parliament Square in protest at his continued detention.

Protesters will hold a vigil and begin their hunger strike outside Parliament once it is officially opened by the Queen on Wednesday.

Battersea resident Shaker Aamer, 44, whose family still live in the area, has been on his own hunger strike in protest against the treatment of his fellow inmates for more than 11 weeks.

Reports from his US lawyer suggest the situation has become so precarious prison authorities are force-feeding him to prevent starvation.

A debate was held in Parliament last week, led by Battersea MP Jane Ellison demanding answers from Foreign Minister Alastair Burt.

Although the required answers were not forthcoming, the debate has given Mr Aamer’s potential release huge political momentum this side of the Atlantic.

Ms Ellison was due to meet Foreign Secretary William Hague with other MPs from last week’s debate, to examine practical steps the Government and Parliament can take.

She said: “My objectives for a further debate would be, firstly, to keep the issue in the forefront of people’s minds, but secondly to pass a motion, hopefully unanimously, that calls upon the US authorities to release Shaker Aamer back to the UK.

“That way Parliament is throwing greater weight behind Foreign Office ministers in their discussions with US counterparts and underlining the fact that Mr Aamer's situation is not accepted in Britain.”

Sadiq Khan, Tooting MP and Shadow Justice Minister, has campaigned for Mr Aamer’s release for many years.

He said: “It is crucial pressure is put on the American government to release Shaker and close down Guantanamo Bay once and for all.

“The public can also do their bit by writing to the USA Embassy to let them know the strength of feeling and to David Cameron to insist that whenever there are discussions between the UK and USA, Shaker’s case is raised and strong representations are made for him to be transferred back to London.”

There has also been further encouragement across the Atlantic where influential Democratic Senator Dianne Feinstein, chairwoman of the Senate intelligence committee, has pushed the White House to show greater urgency regarding prisoners cleared for transfer from Guantanamo Bay.

Ms Ellison added: “I have already contacted Senator Feinstein and think we should be emphasising to key US politicians like her that Britain, a trusted ally, can help the US bring the President's stated aim of closing Guantanamo Bay one man closer to fruition.”

Mr Aamer, a father-of-five, was captured in Afghanistan in 2002 and has been held in the Cuban detention centre for more than a decade without trial or even a charge – it is alleged he has been tortured while incarcerated.

An e-petition, which has hit 117,000 signatures, triggered last week’s Parliamentary debate.