A London judge has widened the scope of a US appeal against a block on the extradition of Wikileaks founder Julian Assange from Britain and will hear the renewed bid in late October.

A judge ruled in January that Assange should not be extradited to the United States to face criminal charges including breaking a spying law, saying his mental health problems meant he would be at risk of suicide.

Assange faces 18 criminal charges in the United States of breaking an espionage law and conspiring to hack government computers.

WikiLeaks published a US military video in 2010 showing a 2007 attack by Apache helicopters in Baghdad that killed a dozen people, including two Reuters news staff. It then released thousands of secret classified files and diplomatic cables.

The legal saga began soon afterwards when Sweden sought Assange's extradition from Britain over allegations of sex crimes. When he lost that case in 2012, he fled to the Ecuadorean embassy in London, where he spent seven years.

When he was finally dragged out in April 2019, he was jailed for breaching British bail conditions although the Swedish case against him had been dropped.

The United States had already been given permission to appeal the January ruling on three grounds, but on Wednesday asked that the scope of it be expanded to include a reassessment of the expert evidence used to evaluate Assange's risk of suicide.

Judge Timothy Holroyde said that it was unusual for an appelate court to reconsider evidence from an expert witness when it has been accepted by a lower court.

But he said it was arguable that the appeal court might make a different assessment, given that a key expert had omitted to disclose what he knew about Assange's relationship with his partner Stella Moris.

"It is my view arguable that the... DJ (district judge) erred," he said.

Lawyers for both sides agreed that the full appeal hearing should be scheduled for October 27 and 28.

Assange joined the hearing by video link, wearing glasses, a face mask and a white shirt.

'An innocent man accused of practising journalism'

Julian Assange's partner has described him as "an innocent man accused of practising journalism".

Stella Moris, who has two children by Assange, stood in front of the steps of the High Court and told his supporters: "The US government is exploiting the inherently unfair arrangement between the US and the UK.

"They are exploiting the inherently unfair extradition arrangements with this country in order to arbitrarily prolong his imprisonment. The imprisonment of an innocent man accused of practising journalism."

Julian Assange's partner Stella Moris pictured outside the High Court in London

Ms Moris, who visited Assange at Belmarsh Prison yesterday, added: "For every day that this colossal injustice is allowed to continue, Julian's situation grows increasingly desperate.

"He won the case against the US government seven months ago, yet he remains in Belmarsh Prison - what is this, if not punishment by process?"

She added: "Yesterday, Julian and I were permitted to embrace for the first time in 17 months - throughout my visit in Belmarsh I held his warm hand.

"Julian has been denied the love and affection of his family for so long.

"Julian and the kids will never get this time back. This shouldn't be happening."

Former Labour leader Jeremy Corbyn also joined protesters in front of the High Court ahead of the preliminary hearing.

He said: "The United States seems to have a sort of obsession with people who uncover the truths about US military presence around the world.

"I think they should wind their necks in and let Julian Assange go.

"I hope the court today gives a very clear signal that they will not allow the appeal by the United States and that Julian Assange will be allowed to go free."

He was applauded by protesters who later shouted "free Julian Assange" and "jail the war criminals" to the sound of a beating drum as uniformed police looked on.