Julian Assange has defied a British police order to turn himself in Friday for extradition to Sweden and will remain holed up in Ecuador's embassy, a spokeswoman for the WikiLeaks founder said.

Assange, who has applied for asylum in Ecuador, was served notice on Thursday to surrender himself to a central London police station, but decided not to comply.

"Julian will remain in the embassy under the protection of the Ecuadorian government," Susan Benn of the Julian Assange Defence Fund told reporters outside the embassy in central London.

"Yesterday, Mr Assange was served with a letter from the Metropolitan Police Service requesting that he surrender himself to Belgravia police station at 11:30 this morning.

"Mr Assange has been advised that he should decline to comply with the police request.

"This should not be considered any sign of disrespect.

"Under both international and domestic UK law, asylum assessments take priority over extradition claims.

"The issues faced by Mr Assange are serious. His life and liberty, and the life and liberty of his organisation and and those associated with it, are at stake."

Benn said Assange was in 'good spirits'.

The embassy is a flat in a mansion block in the plush Knightsbridge district of central London, across the street from the famous Harrods emporium.

A dozen or so demonstrators stood outside holding placards reading 'Free Assange'. The building railings are covered in posters supporting him. A couple of police officers are stationed outside the block.

Jim Curran, secretary of the Civil Rights International group, said he had been demonstrating there most days since Assange sought refuge.

"I am opposed to all political extradition and I believe that is what Assange's case is," he told AFP.

"He has placed himself in a position where he has no other option but to seek asylum. Now that he has taken that course I think that Ecuador should grant him it."

He faces allegations in Sweden of sexual assault and rape against two former female volunteers at his WikiLeaks anti-secrecy website and was arrested on an extradition warrant in December 2010.

He was bailed and embarked on a marathon round of court battles, but finally exhausted all his options under British law earlier this month when the Supreme Court overturned his appeal against extradition.

Following the end of his legal challenges, he was given until Thursday to make a final appeal to the European Court of Human Rights, at which point extradition procedures in Britain could commence.

Assange says he fears that from Sweden he will be extradited to the United States to face possible espionage charges, having released more than 250,000 US diplomatic cables on WikiLeaks.

He sought refuge at Ecuador's embassy in London on June 19, asking for political asylum.

He has therefore breached his bail conditions - which state he must be at a given address between 10:00 pm and 8:00 am - and is liable for arrest.

A Scotland Yard spokesman said officers 'served a surrender notice' upon him Thursday, which required him to go to Belgravia police station.

"This is standard practice in extradition cases and is the first step in the removal process. He remains in breach of his bail conditions. Failing to surrender would be a further breach of conditions and he is liable to arrest."

However, while he remains in the embassy, he is beyond the reach of British authorities.

In a statement Thursday, the embassy said Britain's Foreign Office had written to them reaffirming their commitment to 'promoting excellent bilateral relations' between the two countries.

"The government of Ecuador will continue to foster good relations with the UK government whilst assessing Mr Assange's application for asylum," it added.