Julian Assange will spend his first full day in the Ecuadorian embassy in London since being granted political asylum by the South American country's government.
On Thursday, the WikiLeaks founder described the move as a "significant and historic victory", but Foreign Secretary William Hague made it clear that Mr Assange would not be allowed safe passage out of the country.
The Australian has been taking refuge in the Ecuadorian embassy for the past two months after facing extradition to Sweden on allegations of sexual assault. He denies the claims and fears being sent to the United States if he goes to Sweden.
Mr Hague said that Mr Assange would not be allowed safe passage out of the UK despite the asylum decision, and that diplomatic immunity should not be used to harbour alleged criminals.
Mr Hague said it is a "matter of regret" that the Ecuadorian government granted the WikiLeaks founder political asylum but warned that it "does not change the fundamentals" of the case. The case could go on for some "considerable" time, Mr Hague said, adding: "We will not allow Mr Assange safe passage out of the United Kingdom, nor is there any legal basis for us to do so."
Ecuadorian ministers earlier accused the UK of threatening to attack the embassy to seize Mr Assange, after it emerged that the Diplomatic and Consular Premises Act 1987 could allow revocation of a building's diplomatic status if the foreign power occupying it "ceases to use land for the purposes of its mission or exclusively for the purposes of a consular post".
Under international law, diplomatic posts are considered the territory of the foreign nation. But Mr Hague said: "There is no threat here to storm an embassy. We are talking about an Act of Parliament in this country which stresses that it must be used in full conformity with international law."
The Swedish foreign ministry said it has summoned Ecuador's ambassador over the Latin American country's "unacceptable" decision to grant asylum.
News that Mr Assange had been granted asylum was greeted with cheering by protesters kept behind railings across the road from the embassy in Knightsbridge.
The Union of South American Nations (UNASUR) has convened an "extraordinary meeting" in Ecuador on Sunday to discuss the situation at the embassy.