Human rights barrister Geoffrey Robertson has described secret recordings of himself and other lawyers meeting with Julian Assange as an "illegal" privacy breach — but also a potential "lifeline" for the WikiLeaks founder.

Key points: Julian Assange will face an extradition hearing this evening, Sydney time

Julian Assange will face an extradition hearing this evening, Sydney time It comes a day after it was revealed that Assange had been secretly recorded during legal meetings

It comes a day after it was revealed that Assange had been secretly recorded during legal meetings Geoffrey Robertson, who is shown in the footage, has spoken out ahead of the hearing

Assange is due to face an extradition hearing later today relating to US criminal charges over his role in WikiLeaks' releases of classified US Government material.

The ABC yesterday revealed Assange's conversations — including legally privileged meetings with Robertson and other Australian lawyers — were secretly recorded inside his former home in the Ecuadorian embassy in London.

A video extract shows Robertson arriving at the embassy and beginning a meeting with Assange.

The recordings and other surveillance were allegedly passed on to American intelligence.

Speaking to ABC Radio Adelaide this morning, Robertson described the recordings as a "breach of privacy, a breach of lawyer confidentiality" and "illegal".

However, he said they could actually benefit Assange's case, and drew a parallel with the legal fallout to the leaked Pentagon Papers — which revealed the nature and extent of US military tactics during the Vietnam War — in the early 1970s.

"It may well end Julian Assange's extradition ordeal, because certainly if he gets to America — this is how the Pentagon Papers ended, when they were found to have burgled the psychiatrist who was dealing with [whistle-blower] Daniel Ellsberg, and they had to drop the case," Robertson said.

"I've been on secret police files before, I've been followed by police — secret police — I've been spied on … in communist countries for the most part during the Cold War when I was defending dissidents, but I think this will probably prove to be a step too far.

"It may be the lifeline for Julian Assange because he's facing charges of up to 175 years in prison."

Robertson drew a parallel between the current state of the case and the Pentagon Papers. ( ABC Radio - Conversations )

Assange — who is being represented by Robertson's legal firm — was expelled from the Ecuadorian embassy in April last year after seven years in self-imposed exile, and Robertson said Assange "knew it was coming".

"[US Vice-President] Mike Pence had just been in Ecuador giving a massive loan to the Ecuadorians, and [Assange] said 'I'm going to be the collateral'," Robertson told ABC Radio Adelaide.

"A few days later he was expelled and there was whole black propaganda which I knew to be false about how disrespectful he was and how dirty and smelly he was, and how he smeared excrement on the embassy walls, and this was all lies.

"He has been demonised by the authorities and it will be essential to provide him with a fair trial here [in the UK] and, if it goes that far, America."

Assange might be pardoned if Trump loses, Robertson says

WikiLeaks has previously warned that Assange had been the subject of a sophisticated spying operation inside the embassy.

The organisation said video, audio, photographs and copies of private legal documents and a medical report had turned up in Spain.

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Supporters of Assange rallied in London over the weekend, including former Greek finance minister Yanis Varoufakis and former Pink Floyd frontman Roger Waters, who urged Prime Minister Boris Johnson to make a public statement.

"Come on Prime Minister, be the British bulldog that you would have us all believe you are," Waters declared.

"Call off this show trial, this charade, this kangaroo court."

South Australian senator Rex Patrick yesterday said the revelation of "US bugging" had shed doubt on the "prospect of fair trial in the US".

A spokeswoman for the Foreign Affairs Department said the Government had engaged with the UK over the matter and "sought relevant assurances on multiple occasions".

Robertson said Assange would be unlikely to receive justice under the current US administration, and expressed concerns about the impact of the ongoing saga on his mental health.

Julian Assange arrives at Westminster Magistrates' Court in 2019. ( PA: Victoria Jones via AP )

"He won't be pardoned by President Trump, although [a future] President Sanders might do so," Robertson said.

"I think that's the objective of the Pentagon — to put him in prison for the rest of his life.

"Let's remember that it was 10 years ago when he released information about helicopter killing of Reuters journalists … [and] he released information about how the Americans were killing more civilians in Afghanistan than they were admitting."