Wikileaks founder Julian Assange has been denied access to evidence and even basic items like paper and pens by British prison officials, putting his US extradition case on the brink of judicial review, his lawyer has warned.

Solicitor Gareth Pierce was shocked to learn that District Judge Vanessa Baraitser only intended to allow the defence team one hour to review evidence with the Australian in the holding cells at the Westminster Magistrates Court on Monday.

He's been charged in the US with 17 counts of spying and one count of computer hacking after WikiLeaks allegedly tried to help US army intelligence analyst Chelsea Manning conceal her virtual identity in the release of thousands of classified Pentagon files regarding the Iraq and Afghanistan wars.

Some of those files have revealed US war crimes committed in both countries.

Assange's supporters in the public gallery, including British rapper M.I.A., silently waved and raised fists to him and he smiled and nodded before giving them a two-fingered salute.

Ms Pierce, who had expected to have a full day with Assange, explained that her team had previously been allowed just two hours to review evidence with him in prison.

"It set us back in our timetable enormously," she told the court.

"We will do our best but this slippage in the timetable is extremely worrying."

Ms Pierce described how the administration of Belmarsh prison, where he's being held, had obstructed access to her client to the point where she had even had to approach UK government lawyers to assist.

She warned that further denying Assange his "human right" to legal access was putting his case on the brink of a judicial review.

Judge Baraitser adjourned the case until later on Monday afternoon to allow the defence team to review case evidence with Assange.

In that second sitting, Ms Peirce said that she had only had an hour to speak to Assange.

Wikileaks ambassador Joseph Farrell called Assange's severely limited access legal representation to date as outrageous.

"Given the way Belmarsh is dealing with this, it's on the brink of judicial review," he told AAP.

"To have three hours with your lawyers when you're facing 175 years in prison (in the US) is not acceptable."

Academy and Grammy award-nominated hip-hop artist M.I.A., who visited Assange in prison last year, said authorities had even denied him simple things like a pen and paper.

She said some books were denied as well due to concerns he could use them to secretly communicate with outsiders.

"It blows my mind that England can have this going, and with the support of Australia," M.I.A. told AAP.

Mr Farrell said given the amount of stumbling blocks presented to Assange it raised the question of whether the "biggest media freedom case this century" was actually a fair trial.

"More importantly than all that, the fact that this is a trial at all is outrageous," he told AAP.

"This is somebody who is in prison for exposing war crimes, for doing his job. He's in prison for the very same reason as he was given a Walkley Award. This is not something that should be allowed to happen."

Assange's next hearing is scheduled for January 23. He is due to appear via video link from Belmarsh prison.

Full extradition proceedings are expected to commence in February.