The government's proposed Justice and Security Bill must be amended to curb the insidious powers of the security services, Parliament has heard.
As British resident Shaker Aamer marked 11 years in Guantanamo Bay today, Green MP Caroline Lucas tabled amendments to the Bill.
Ms Lucas's amendment states that where a claim has been made to the Intelligence and Security Committee (ISC) about the actions of the secret services which are false and which harm the individual being defamed, then the ISC must immediately investigate the claim and ensure that the misinformation is corrected.
Mr Aamer has told his lawyer, Reprieve director Clive Stafford Smith, that British agencies have made defamatory statements about him which he believes prevent him from being released.
Ms Lucas said: "The defamation of Shaker Aamer is evidence of the immense power of the security services to say whatever they want about an accused man, to devastating effect.
"The failure of the British government to challenge this illegal incarceration is shameful and damaging."
Despite having been cleared for release under both the Bush and Obama administrations, Mr Aamer remains imprisoned and has never met his youngest child.
Mr Stafford Smith said: "Surely after he has spent 11 years in that terrible prison without charges or trial, cleared for release for six years, he should be allowed home to London to meet his youngest child Faris for the first time," he said.