Julian Assange says he will leave the Ecuadorean embassy in London and accept arrest by British police tomorrow if he loses a last-ditch attempt to clear his name.

Key points: If his appeal is unsuccessful, Assange says he will leave the embassy at noon tomorrow

If his appeal is unsuccessful, Assange says he will leave the embassy at noon tomorrow If successful, Assange wants his passport returned and arrest attempts to stop

If successful, Assange wants his passport returned and arrest attempts to stop He has been living in the Ecuadorean embassy in London since June 2012

The United Nations has been investigating whether the Australian founder of WikiLeaks has been illegally detained, and is due to hand down its findings within the next day.

Mr Assange has been living in the embassy since June 2012 after being granted asylum by Ecuador.

In a statement published on Twitter by WikiLeaks, he said if he lost the case against the United Kingdom and Sweden, he would "exit the embassy at noon on Friday (GMT) to accept arrest by British police, as there is no meaningful prospect of further appeal".

But Mr Assange said if his UN case was successful, he expected the "immediate return" of his passport "and the termination of further attempts to arrest me".

He is wanted for questioning by Swedish police over an alleged sexual assault.

Mr Assange has denied the allegation and claims it forms a bid to extradite him to the United States over the leaking of sensitive diplomatic cables.

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In October last year, British police ended their 24-hour guard of the embassy.

Instead they said they would focus on a "covert plan" to prevent Mr Assange's departure.

Today, a spokesman for British police said the Metropolitan Police Service would arrest Mr Assange if he did leave.

"The warrant is still in place. If he leaves the embassy we will make every effort to arrest him," they said.

Greens senator Scott Ludlam said the Federal Government needed to put pressure on the United Kingdom.

"Irrespective of what the UN working group decides, the Australian Government should be arguing strongly that Mr Assange gets his passport back, that he's given safe passage to Ecuador if that's where he wants to go and that the United States Government should stand down that Department of Justice investigation," Senator Ludlam said.

"I think he's got a very strong case that he's been unlawfully and arbitrarily detained.

"It's a very high-stakes situation now."