LONDON (REUTERS) - Britain on Friday (Feb 5) said it would contest a United Nations panel opinion that Wikileaks founder Julian Assange was a victim of arbitrary detention and said the computer hacker would be arrested if he left the embassy.

"This changes nothing. 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," a government spokesman said.

"He is, in fact, voluntarily avoiding lawful arrest by choosing to remain in the Ecuadorean embassy," the spokesman said. "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."

Assange should be allowed to go free from the Ecuadorian embassy in London and awarded compensation for what amounts to a three-and-a-half-year detention, a UN panel ruled on Friday (Feb 5).

British Foreign Secretary Philip Hammond poured scorn on the report, calling it ridiculous, and said the Wikileaks founder was a fugitive from justice. "I reject the decision of this working group," Hammond told ITV news on Friday (Feb 5).

"It is a group made up of lay people and not lawyers. Julian Assange is a fugitive from justice. He is hiding from justice in the Ecuadorian embassy. "He can come out any time he chooses... But he will have to face justice in Sweden if he chooses to do so. This is frankly a ridiculous finding by the working group and we reject it."

Assange, 44, a computer hacker who enraged the United States by publishing hundreds of thousands of secret US diplomatic cables, has been holed up in the embassy since June 2012 to avoid a rape investigation in Sweden.

Both Britain and Sweden deny that Assange is being deprived of freedom, noting he had entered the embassy voluntarily.