A slew of public celebrity support has given Julian Assange’s father hope the WikiLeaks founder will avoid extradition to the US.

About 500 people rallied in support of Assange at a gathering in London on Saturday, pre-empting the start of the extradition hearing on Monday that will determine his fate.

Pink Floyd’s Roger Waters, The Pretenders’ Chrissie Hynde and Brian Eno joined Greek politician and writer Yanis Varoufakis, British Iraqi rapper Lowkey and fashion designer Vivienne Westwood at the protest at Parliament Square.

John Shipton, Assange’s father, hopes the display of support will spur the UK government into intervening in the case.

“What I perceive is an upwelling amongst the people of support – a historical moment of change that will ensure the government of the United Kingdom can act firmly in their own interests,” Mr Shipton told AAP.

“So that the … plague of malice that emanates from the Crown Prosecution Service, and brings into disrepute the administration of law in the United Kingdom, can be stopped and Julian’s freedom can come.”

• Related story: The day I spent with Julian Assange

Earlier in the week, Hynde publicly addressed US President Donald Trump, said she was standing up against further punishment against a man who was protecting freedom.

“I know Mr Assange broke the law (as I have done defending the treatment of animals) but I believe he has been duly punished and should now be set free,” she wrote via Twitter.

An open Letter to @realDonaldTrump, President of the United States.

Dear Mr. President,

I often think of how much my father, Melville “Bud” Hynde, who proudly served his country as a Marine on Guadalcanal, would have enjoyed your Presidency. [p1.]

— Chrissie Hynde (@ChrissieHynde) February 17, 2020

Assange’s trial will begin his legal battle against extradition to the US, where he faces 17 spying charges and one charge of conspiring to commit computer intrusion – charges that carry a total prison sentence of 175 years.

They relate to WikiLeaks’ 2010 publication of thousands of classified Pentagon files on the Iraq and Afghanistan wars – some that revealed war crimes and the torture of prisoners – along with US diplomatic cables.

Meanwhile, at the rally, Rapper Lowkey lashed out at UK newspapers, which he accused of gaining advertising sales by publishing WikiLeak’s disclosures but failing to publicly defend Assange.

“How many oil adverts were put on the pages of The Guardian on the back of Julian Assange’s stories and works for WikiLeaks?” he told the crowd.

The Pretenders frontwoman Chrissie Hynde plays to the crowd on Saturday. Photo: AAP

“How much money did these same newspapers that are hanging him out to dry, that are clamouring for his execution, how much money have they got from major oil companies that advertise on their pages?”

Mr Varoufakis, who plans to visit Assange in London’s Belmarsh prison on Sunday, urged ralliers not to let the WikiLeaks founder turn into “a latter-day Man in the Iron Mask”.

“We are in the business of allowing unalloyed, unarmed truth to have the final word, we are in the business to ensure Julian’s sentence will end neither with a bang or with a whimper, but with a magnificent full stop,” he said.

-with AAP