Sydney: The mother of WikiLeaks founder Julian Assange says she is fearful a British court will allow his extradition to Sweden, saying "the biggest governments in the world are gunning for him".

Australian Assange, 40, will learn on Wednesday whether he will be sent to Sweden where he is wanted for questioning over allegations of rape and sexual assault, when the Supreme Court hands down its judgement in the complex case.

His mother Christine Assange, who has jetted to London for the decision by Britain's highest court, which is her son's last avenue of appeal following numerous legal battles, said waiting for the ruling was a painful experience.

"It's a 24-hour nightmare because we know he is not safe and the biggest governments in the world are gunning for him," she told Australia's Network Seven late on Tuesday.

"If the decision is against him, within 10 days he will be in a Swedish prison."

Assange shot to global fame after his WikiLeaks site enraged Washington by leaking thousands of secret US documents on the wars in Iraq and Afghanistan. The site later leaked thousands of US diplomatic cables.

He believes his extradition to Sweden could pave the way for extradition to the US on possible espionage or conspiracy charges relating to the leaked documents.

His mother said the rape and sexual assault allegations against her son, who has been under virtual house arrest in London for more than a year without charge, were unfounded.

"I don't believe they're true and neither does anybody else," she said.

Nevertheless, she fears his extradition to Sweden where she believes he could be held "incommunicado, in solitary confinement, before he is even questioned or charged".

She said the legal process he had been subjected to have been "extremely unfair" and that she was even more concerned about what would happen if he was sent to the United States.

"How I feel? I feel.. a mix of anger, outrage and fear," she said.

Assange was detained in December 2010 on a European arrest warrant relating to allegations he raped one woman by having sex with her while she was asleep, and sexually assaulted another, in Sweden.

The former computer hacker insists the sex was consensual and the allegations politically motivated.

His case rests on a single point -- that the Swedish prosecutor who issued a warrant for his arrest was not a valid judicial authority.

(Agencies)

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