The Government is facing fresh pressure to resolve the case of Julian Assange after a United Nations working group confirmed that the WikiLeaks founder is being "arbitrarily detained" in the Ecuadorian embassy in London.
The UN Working Group on Arbitrary Detention called on the Swedish and British authorities to end Mr Assange's "deprivation of liberty".
The panel added that the authorities should respect his physical integrity and freedom of movement.
Mr Assange has been living in the embassy for more than three years after being granted political asylum by the Ecuadorian government.
He is wanted for questioning over an alleged sex offence in Sweden, which he denies.
Mr Assange believes he will be transported to the United States to be quizzed over the activities of WikiLeaks if he is extradited to Sweden. There is an espionage case against him in the US.
He filed a complaint against Sweden and the UK in September 2014 which has been considered by the UN Working Group on Arbitrary Detention.
"The Working Group on Arbitrary Detention considers that the various forms of deprivation of liberty to which Julian Assange has been subjected constitute a form of arbitrary detention," said Seong-Phil Hong, who heads the expert UN panel.
"The Working Group maintains that the arbitrary detention of Mr Assange should be brought to an end, that his physical integrity and freedom of movement be respected, and that he should be entitled to an enforceable right to compensation."
Mr Assange's legal team is due to give a news conference in central London later today.
A statement issued in Geneva by the UN panel said: "In its official opinion, the UN Working Group considered that Mr Assange had been subjected to different forms of deprivation of liberty - initial detention in Wandsworth Prison in London, followed by house arrest and then confinement at the Ecuadorian embassy.
"The experts also found that the detention was arbitrary because Mr Assange was held in isolation at Wandsworth Prison, and because a lack of diligence by the Swedish Prosecutor's Office in its investigations resulted in his lengthy loss of liberty.
"The Working Group established that this detention violates Articles 9 and 10 of the Universal Declaration on Human Rights, and Articles 7, 9(1), 9(3), 9(4), 10 and 14 of the International Covenant on Civil and Political Rights."