Julian Assange will never be allowed free passage out of Britain, the Government said tonight, raising the prospect of the fugitive Wikileak founder’s effective imprisonment inside the Ecuadorean embasssy in Knightsbridge for months or even years to come.

Ecuador threw down the gauntlet to the UK, Sweden and the United States today by granting political asylum to Mr Assange, who has been holed up in its cramped embassy on the ground-floor of 3 Hans Crescent, London, for the past two months, avoiding extradition to Sweden to face questioning on allegations of rape.

Following a dramatic day which saw protests, arrests and an increasingly ugly diplomatic fall-out between the UK and Ecuador, the South American country’s foreign minister said it was granting asylum to Assange, 41, because of “serious indications” that the United States could threaten the Australian’s “security, integrity and even his life”.

Officials in Washington are furious that Mr Assange published thousands of confidential US diplomatic cables online, and some Republican politicians have called for the death penalty if he ever faces espionage charges in America.

Britain insists that nothing has changed now that he has been granted asylum. He can only leave the embassy and travel to Quito if Britain agrees to allow him safe passage to an airport.

Quito has warned that any attempt to enter the embassy and seize Mr Assange would constitute an assault on Ecuador’s sovereignty and would be tantamount to an “invasion”.

Tonight, in an announcement that sparked rumours that Mr Assange might be willing to court arrest, WikiLeaks indicated that its founder would give a statement at 2pm on Sunday “outside the Ecuadorian embassy”.

The brief statement, uploaded onto Twitter, was surprising because it has generally been assumed that diplomatic immunity ends at the entrance to the embassy, not the front door of the building.

The mansion block which holds the Ecuadorian embassy is also home to the Colombian embassy and a host of luxury flats meaning police could arrest Mr Assange as soon as he steps into the lobby.

A crisis in relations with much of South America is brewing as a result of the Foreign Office’s earlier apparent threat to snatch the Wikileaks founder from the Ecuadorian embassy.

Foreign Office officials must now try to solve the conundrum of going about arresting Mr Assange without sparking an international crisis.

David Cameron, who is on holiday in Spain, also contacted the Foreign Office today amid fears the department had blundered by issuing the warning to Ecuador.

The deepening acrimony between the two countries is poisoning British relations with other nations in South America. Argentina, Bolivia and Venezuela – all hostile to the UK – already back Ecuador, and the Government anxiously awaits the reaction of the continent’s superpower, Brazil.

Whitehall sources admitted that an apparent threat – delivered by a diplomat in the Ecuadorian capital Quito – to raid the London embassy had inflamed the situation.

The Foreign Secretary William Hague, asked tonight whether the impasse could last for months or even years, said: “It could. It is, above all, a difficulty for Ecuador and for Mr Assange but this is a strange position for an embassy to be in this position.

“Diplomatic immunity exists to allow embassies and diplomats to exercise proper diplomatic functions. The harbouring of alleged criminals, or frustrating the due legal process in a country, is not a permitted function.”

Mr Hague said Mr Assange’s rights were “guaranteed” and this should be enough for Ecuador: “We are committed to work with Ecuador amicably... we cannot give safe passage to somebody in this situation.” He tried to play down Ecuadorian fears that British police plan to forcibly enter the building: “There is no threat here to storm an embassy.”

The founder of the world’s most famous online whistleblowing platform fled to Ecuador’s embassy 59 days ago after the last of his legal appeals to stop his extradition to Sweden on rape allegations was exhausted.

Mr Assange has insisted that such drastic action was necessary not to avoid a potential prosecution in Sweden, but because he feared a further extradition to the US. Sweden remains convinced that Mr Assange is simply trying to avoid questioning over charges that he raped two women during the summer of 2010, an allegation he denies.

There were suggestions that Mr Assange could try and engineer an escape either in a diplomatic bag or a vehicle but in practice it would be difficult to engineer, given the permanent police presence outside the embassy. Although diplomatic cars and bags cannot be searched Mr Assange would still need to exit when he got to an airport and could then be arrested. An attempt by the Nigerians to smuggle a national out of the country in the late 1980s was uncovered by UK police, causing the Nigerians significant embarrassment.

Ecuador could try to give Mr Assange immunity status by appointing him a member of the embassy staff but the British government must approve all diplomatic appointments and would not do so in Mr Assange’s case.

In a statement released online the WikiLeaks founder added: “I’m grateful to the Ecuadorean people, President Rafael Correa and his government. It was not Britain or my home country, Australia, that stood up to protect me from persecution, but a courageous, independent Latin American nation. While today is a historic victory, our struggles have just begun.”