"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 Assange to Sweden," a UK government spokesperson said.
The UK government statement comes a day ahead of a ruling by the UN' Working Group on Arbitrary Detention on whether the time the 44-year-old Australian national spent inside the Embassy amounts to illegal detention.
Earlier, Assange had promised to surrender to the police if the UN panel rules that the three years he was holed up inside the Embassy does not amount to illegal detention.
In a statement issued by Wikileaks on Twitter, he said: "Should the UN announce tomorrow that I have lost my case against the UK and Sweden, I shall exit the embassy at noon on Friday (February 5) to accept arrest by British police as there is no meaningful prospect of further appeal.
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Assange was granted political asylum by the Ecuador government in 2012.
In 2014, he complained to the UN that he was being "arbitrarily detained" as he could not leave without being arrested.
The UK Foreign Office, on the other hand, claimed Assange had voluntarily avoided lawful detention, saying it still had an obligation to extradite him.
Scotland Yard also said the arrest warrant against Assange remains in place and he is likely to be arrested if he decides to step out of his hideout.
He is wanted for questioning in Sweden over rape and sex assault allegations against two women, which he has always denied.
Last month, it emerged that Assange will be questioned by Swedish authorities over the allegations at his Ecuadorean embassy hideout in London.