Foreign Secretary Philip Hammond has attacked the UN expert panel as a working group "made up of lay people and not lawyers" who have produced a "frankly ridiculous" ruling on Julian Assange.
The five person panel - officially known as the Working Group on Arbitrary Detention - became a four-man panel after the group's only woman dropped out citing a potential conflict of interest in the case.
The decision to rule against the UK and Sweden in the case - finding the WikiLeaks founder arbitrarily detained by the two governments' threat of legal action - did not prove unanimous though.
Who is on the five-person panel?
Current head of the panel Seong-Phil Hong, who was appointed to the working group in May 2014, led the group's opinion that Julian Assange had been detained arbitrarily by the UK and Sweden. The Korean teaches law, human rights and ethics in investment at Yonsei Law School in Seoul and has given his expertise in relation to the Asia Pacific Forum and World Bank. His work on human rights has included cases involving North Korea and enforced sex slaves from the Second World War.
The group's longest-standing member, Ukrainian Vladimir Tochilovsky, was the only dissenting opinion in the panel, claiming its agreed ruling raises a "serious question as to the scope of the working group" in ruling over Mr Assange's restriction of liberty. He argued Mr Assange fled bail and had used the Ecuadorian embassy as a safe haven since 2012, effectively agreeing with the position held by the UK and Swedish authorities. Mr Tochilovsky also said issues related to Mr Assange's "self-confinement, such as asylum and extradition," were outside of the group's mandate. Mr Tochilovsky is an expert on international criminal justice and human rights in criminal justice and worked in several roles at the UN and International Criminal Court before joining the working group in May 2010.
José Guevara agreed with the panel's opinion that Mr Assange had been detained unlawfully. Guevara joined the working group in June 2014 and is the first vice-chair. The Mexican has been recognised in his homeland and internationally for his work in human rights and criminal law, including roles for the International Criminal Court and the Mexican Ministry of Foreign Affairs.
The group's second vice-chair Sètondji Adjovi also agreed with the panel's opinion that Mr Assange had been arbitrarily detained. He was appointed in May 2014 teaches African affairs and international law, including human rights, at Arcadia University in the US state of Pennsylvania. He has also worked at the International Criminal Court and at the International Criminal Tribunal for Rwanda.
Leigh Toomey, the panel's only woman, was appointed in August 2015 but opted against taking part in the deliberations on the Assange case because she too is an Australian citizen and feared a perceived conflict of interest. An expert in human rights and justice, Ms Toomey has worked extensively at the UN and Human Rights Council.
The working group's history
The UN's Working Group on Arbitrary Detention (WGAD) was established in 1991 to investigate whether states are in compliance with human rights obligations.
It has ruled on hundreds of cases concerning international laws like the UN Declaration on Human Rights, the European Convention on Human Rights and the UN Standard Minimum Rules for the Treatment of Prisoners.
WGAD receives submissions from a complainant and respondents and decides whether the case amounts to unlawful detention.
Burmese stateswoman Aung San Suu Kyi is among a number of high profile complainants who have been supported by the group's rulings.
Julian Assange filed a complaint against Sweden and the UK on September 12 2014, with the two countries responding in November of that year.