An expert in UK extradition law says it's “very likely” that WikiLeaks founder Julian Assange will lose his battle against extradition to Sweden, where he's wanted for questioning in an investigation into rape and sexual assault allegations.

Julian Knowles, a barrister for law firm Matrix Chambers and the author of books on extradition, told BBC Radio that the legal and factual bases underpinning Assange's defense during three days of extradition hearings in London earlier this month weren't persuasive. As a result, Chief Magistrate Judge Howard Riddle, who is scheduled to deliver his judgment on Thursday, is likely to rule in favor of Swedish prosecutors seeking Assange's extradition, he said.

“From what I read and heard about the Assange extradition hearing, I think it's very likely that the Swedish prosecutor will prevail and extradition will be ordered by the senior district judge,” Knowles said during an interview on BBC Radio's Law in Action program. “In a nutshell, the two preliminary arguments that the defense are running are (one) the prosecutor has no power to issue the warrants and (two) that Mr Assange is only really wanted for questioning and isn't really wanted for trial and you have to be wanted for trial in order to be properly extradited.”

Knowles went on to say: “There is no doubt that a Swedish prosecutor does have the power to issue warrants.” He also said that the Swedish prosecutor handling the case “has made clear that Mr Assange is wanted for trial if he goes back. Unless he can demonstrate his innocence ahead of trial, he will be tried.”

Knowles shot down other claims made by Assange's legal team, including the argument that the alleged behavior being investigated, even if true, didn't amount to extradition offenses. Allegations leveled by one of Assange's accusers involve the use of force and would “obviously” constitute sexual assault if tried in the UK.

Assange has admitted having sex with two women while visiting Sweden in August, but says the relations were consensual. He has cited evidence that the accusers sought revenge and that the probe is politically motivated by his site's airing of confidential US documents.

Law in Action's Joshua Rozenberg also spoke to the US justice department's attaché to the US embassy in London, who dispelled claims Assange might face detention in Guantanamo Bay prison or even the death penalty if ultimately extradited to the US. American officials have confirmed they are working to build a case against Assange, but have yet to bring any charges against him.

No matter which side prevails in the extradition fight, the losing party will almost certainly appeal and set off what could be months or years of proceedings, Knowles said. In the event the US seeks Assange's extradition before he is transferred to Sweden, it will be up to the UK's Home Secretary, Theresa May, to decide which of the two requests to honor. Knowles predicted the US application would win the day.

Assange remains under house arrest in a country estate outside London and must adhere to strict rules that require him to report daily to police. He is expected to attend Thursday's hearing in Belmarsh Magistrates Court in south-east London.

The legal prognosticating comes as WikiLeaks began a new campaign to raise funds to pay Assange's legal bills by hawking T-shirts, mugs and stickers bearing his image. One of them casts the founder as a Che Guevara figure with the words "Viva la Informacion" as the slogan.