WikiLeaks editor-in-chief Kristinn Hrafnsson says the sentence for breaching bail does little to engender confidence in Assange's continued legal fight against extradition to the US.

Hrafnsson spoke to a crowd packed with journalists and supporters outside Southwark Crown Court on Wednesday after Assange was sentenced to 50 weeks in prison for the bail breach.

Assange had been warned last month on conviction that the maximum sentence for such an offence was 12 months.

"It is my view as editor of WikiLeaks that this sentencing here today is an outrage and it's vindictive in nature," Hrafnsson said.

"It doesn't give us a lot of faith in the UK justice system for the fight ahead.

"To get a sentence only two weeks short of the maximum sentence is an outrage."

He also drew a comparison with the sentence of British speedboat killer Jack Shepherd who fled the UK after being convicted.

"And may I point out, just in comparison, that the so-called speedboat killer got six months for not showing up in court to hear his sentencing for manslaughter," the editor said.

Shepherd was given credit for his guilty plea while Assange denied the bail offence and was convicted by a court.

Hrafnsson described the challenge of opposing extradition, which will begin with a hearing at Westminster Magistrates' Court on Thursday, in dramatic terms.

"It will be a question of life and death for Mr Assange," he said, calling it the "big fight".

He added: "It's also a question of life and death for a major journalist principle."

Assange's lawyer Jennifer Robinson said: "Today is the first time that a British court has heard detailed evidence about the concerns and the fears that led Mr Assange to seek asylum inside the Ecuadorian embassy."

She encouraged people to read the submissions made to the court, which she said would be made public, and to "come to your own conclusion about that evidence and the reasonableness of his decision to go inside the embassy when he chose to do so".

Australian Associated Press