A diplomatic row is brewing over claims that the Government was threatening to enter the Ecuadorian embassy in London and arrest WikiLeaks founder Julian Assange, who is seeking political asylum.
Ecuador's minister for foreign affairs, Ricardo Patino, released details of a letter he said was delivered through a British embassy official in the capital of the South American country, Quito.
The letter said: "You need to be aware that there is a legal base in the UK, the Diplomatic and Consular Premises Act 1987, that would allow us to take actions in order to arrest Mr Assange in the current premises of the Embassy. We sincerely hope that we do not reach that point, but if you are not capable of resolving this matter of Mr Assange's presence in your premises, this is an open option for us."
The dramatic development came two months after Mr Assange suddenly walked into the embassy in a bid to avoid being extradited to Sweden, where he faces allegations of sexual assault.
The Foreign Office says the 1987 law permits the revocation of diplomatic status of a building 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.
Mr Patino said: "Ecuador, as a state that respects rights and justice and is a democratic and peaceful nation state, rejects in the strongest possible terms the explicit threat of the British official communication... This is unbecoming of a democratic, civilised and law-abiding state. If this conduct persists, Ecuador will take appropriate responses in accordance with international law."
An Ecuadorian government spokesman said: "We are deeply shocked by the British government's threats against the sovereignty of the Ecuadorian Embassy and their suggestion that they may forcibly enter the embassy. This a clear breach of international law and the protocols set out in the Vienna Convention."
A Foreign Office spokeswoman denied a threat was being made. The spokeswoman said: "We have consistently made our position clear in our discussions with the government of Ecuador... We are still committed to reaching a mutually acceptable solution."
Police stood watch outside the building housing the Ecuadorian embassy, in London's elegant Knightsbridge area. A handful of protesters gathered overnight, and some sat on the ground at the foot of a small flight of steps leading into the building.
Paul Milligan, 19, from Kentish Town, north London, said: "If they load him in a police van to try to bring him out, I intend to sit in front of the van and obstruct it in any way I can. The idea that somebody can be snatched from the Ecuadorian embassy in London by British police, and sent to Sweden then possibly America, is ludicrous."