Mr Robertson and another specialist extradition lawyer from his Doughty Street Chambers are to act for Mr Assange who was expected to surrender to police late yesterday and appear in a magistrate's court to argue for bail. A full hearing of the extradition case must be heard within 28 days.

But London legal sources warned that the European arrest warrant issued for Mr Assange over sexual assault claims in Sweden is difficult to ''avoid or challenge''. He and his lawyers plan to fight the extradition with every available resource. There is growing fear that this case could lead to a hand-over to US authorities in the wake of the release of hundreds of thousands of US diplomatic cables.

The Age believes that Mr Robertson, whose chambers are one of the few with a specialist in extradition proceedings with Scandinavian nations, has been in contact with Assange about his defence and met federal Attorney-General Robert McClelland about the case.

The imminent surrender of Mr Assange is unfolding as his whistleblower website continued to battle a seemingly global effort to block release of further information led by the US Attorney-General, Eric Holder. Mr Holder said he had authorised significant actions aimed at prosecuting the WikiLeaks founder but he refused to specify what these might be.

''The lives of people who work for the American people have been put at risk. The American people themselves have been put at risk by these actions that I believe are arrogant, misguided and ultimately not helpful in any way,'' he said.

Mr Assange, 39, is reported by The Guardian to be seeking supporters to put up surety and bail to stave off attempts to hold him. He has reportedly told friends he is increasingly convinced the US is behind Swedish prosecutors' attempts to extradite him.

He has previously said that the original allegations were the product of ''personal issues'' but he believes Sweden has behaved as ''a cipher'' for the US.

He is wanted by Swedish detectives after two women claimed they were sexually assaulted by him when he visited the country last August. The Swedish supreme court upheld an order to detain him for questioning after he successfully appealed against two lower court rulings.

Mr Assange has also said he declined to return to Sweden to face prosecutors because he feared he would not receive a fair trial and that prosecutors had requested that he be held in solitary confinement and incommunicado.

But the constant need to be on the move is taking its toll and he has conceded he is becoming exhausted by the battle to keep defending the allegations in Sweden while running the carefully managed release of the US cables.

The site's access to funds is also being slowly squeezed as financial institutions succumb to US and other diplomatic pressure. A Swiss bank said this week that it had shut down Mr Assange's account because he had allegedly given ''false information'' while the US-based PayPal has also frozen the WikiLeaks accounts, stimying the site's ability to raise funds.

American political rhetoric and attacks against WikiLeaks are also escalating with the former vice-presidential candidate Sarah Palin describing Mr Assange as ''an anti-American operative with blood on his hands''.

But in Australia yesterday, Prime Minister Julia Gillard backed away from her comment of late last week that the actions of Mr Assange and WikiLeaks were ''illegal''.

When asked what, under Australian law, was illegal about his actions, she was unable to nominate anything. ''The foundation stone of it is an illegal act,'' Ms Gillard said. The ''foundation stone'' was the initial theft of the cables - allegedly committed by a US army private - and not the publication by WikiLeaks.

''It would not happen, information would not be on WikiLeaks, if there had not been an illegal act undertaken,'' Ms Gillard said.

The opposition's legal affairs spokesman, George Brandis, later called Ms Gillard's use of language clumsy. ''As far as I can see, he [Mr Assange] hasn't broken any Australian law, nor does it appear he has broken any American laws,'' he told Sky News.