A United Nations working group has ruled that WikiLeaks founder Julian Assange is being "arbitrarily detained" in the Ecuadorian embassy in London - and called for him to be paid compensation.
The UN Working Group on Arbitrary Detention said the Swedish and British authorities should end Mr Assange's "deprivation of liberty" and respect his physical integrity and freedom of movement.
However, a Government spokesman said the announcement "changes nothing", adding: "We completely reject any claim that Julian Assange is a victim of arbitrary detention. The UK has already made clear to the UN that we will formally contest the working group's opinion."
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 and is expected to press for him to be allowed to leave the embassy without being arrested.
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."
The panel also called for Mr Assange to be given compensation.
The Government spokesman added: "Julian Assange has never been arbitrarily detained by the UK. The opinion of the UN Working Group ignores the facts and the well-recognised protections of the British legal system.
"He is, in fact, voluntarily avoiding lawful arrest by choosing to remain in the Ecuadorian embassy.
"An allegation of rape is still outstanding and a European Arrest Warrant in place, so the UK continues to have a legal obligation to extradite him to Sweden. As the UK is not a party to the Caracas Convention, we do not recognise 'diplomatic asylum'.
"We are deeply frustrated that this unacceptable situation is still being allowed to continue. Ecuador must engage with Sweden in good faith to bring it to an end.
"Americas Minister Hugo Swire made this clear to the Ecuadorian Ambassador in November, and we continue to raise the matter in Quito."
The Swedish Prosecution Authority said the statement from the UN group had "no formal impact" on its ongoing investigation.
The Metropolitan Police have said they will make "every effort" to arrest Mr Assange should he leave the embassy.