The UK is to make a formal protest to the government of Ecuador over the country’s decision to “harbour” Julian Assange, the Foreign Office has said.
The Wikileaks founder sought asylum in London’s Ecuadorean embassy in 2012 to avoid extradition to Sweden.
Minister Hugo Swire said the bill to the UK taxpayer, which stands at £12m ($18.8m; €16.8m), was “unacceptable.”
Earlier, Swedish prosecutors dropped two sex assault claims against Mr, Assange, who denies the allegations.
Mr. Assange still faces the more serious accusation of rape, which he also denies.
The British Ambassador in Quito, Ecuador’s capital, is to make the formal protest to the Ecuadorean government on Thursday.
“Ecuador must recognise that its decision to harbour Mr. Assange more than three years ago has prevented the proper course of justice,” Swire said.
“As a result, some of the serious sexual allegations against him will now expire. It is completely unacceptable that the British taxpayer has had to foot the bill for this abuse of diplomatic relations.”
Mr. Assange sought asylum to avoid extradition to Sweden, fearing he would then be sent to the US and put on trial for releasing secret American documents.
He remains in the embassy and has previously said he will not leave, even if the accusations of sex crimes were dropped.
The UK has paid for policing around the embassy in Knightsbridge, central London, for the past three years.
Mr. Swire said the UK “continues to have a legal obligation” to extradite Mr. Assange.
The formal protest comes after Swedish prosecutors dropped their investigation into an allegation of sexual molestation and an accusation of unlawful coercion against Mr. Assange because they ran out of time to question him.
An additional alleged incident of sexual molestation will be “time barred” – that is, time will have run out to question Mr. Assange – on August 18.
The Swedish statement also said an allegation of rape was due to expire on August 17, 2020, but that investigation would continue.
The alleged events took place in August 2010.
Mr Assange said he was “extremely disappointed” and said the Swedish prosecutor had avoided hearing his side of the story.
“There was no need for any of this. I am an innocent man. I haven’t even been charged,” said Mr Assange.
“From the beginning I offered simple solutions. Come to the embassy to take my statement or promise not to send me to the United States. This Swedish official refused both. She even refused a written statement.”