The United States Government has won the latest round in its High Court bid to appeal against the decision not to extradite Julian Assange on espionage charges.

Assange, 50, is wanted in America on allegations of a conspiracy to obtain and disclose national defence information following WikiLeaks’ publication of hundreds of thousands of leaked documents relating to the Afghanistan and Iraq wars.

After a multi-week extradition hearing, District Judge Vanessa Baraitser ruled in January that Assange should not be sent to the US, citing a real risk of suicide.

The US Government was previously allowed to appeal against her decision on three grounds, including that it was wrong in law.

On Wednesday, the US made a bid at the High Court to expand the basis that can be used for its main appeal against the district judge’s decision.

The American authorities said they should be allowed to argue two further points – that the district judge was wrong in how she assessed evidence about Assange’s risk of suicide and also appeal against the use of evidence from a psychiatrist who they said “misled” the court.

Lord Justice Holroyde ruled in favour of the US authorities after he found the two points were “at least arguable” at the main appeal, which will take place over two days in October.

The WikiLeaks founder appeared at the hearing by video-link from Belmarsh Prison, wearing a dark face covering and a white shirt, with what appeared to be an untied burgundy tie draped around his neck.

Dozens of Assange’s supporters, including his partner Stella Moris, gathered outside the Royal Courts of Justice on Wednesday morning, chanting and waving signs.

Former Labour leader Jeremy Corbyn was also seen outside the central London building, telling supporters that the US Government should “wind their necks in”.

Clair Dobbin QC, for the US, had told the court there is a “need for anxious scrutiny” of Assange’s reported mental health.

The barrister said part of the US Government’s appeal will focus on the requirement in law that an individual must be “so ill” that they are unable to resist suicide for a decision to be taken not to prosecute – or in Assange’s case, extradite – them.

She said: “It really requires a mental illness of a type that the ability to resist suicide has been lost.

“Part of the appeal will be that Mr Assange did not have a mental illness that came close to being of that nature and degree.”

Ms Dobbin also told the court that the need for scrutiny is “substantially increased” given the background – including the “extraordinary lengths” Assange has already gone to in order to avoid extradition.

The US authorities have also claimed that evidence from Assange’s psychiatric expert, Professor Michael Kopelman, should have been dismissed or had less weight attributed to it.

Ms Dobbin argued the expert “misled” Judge Baraitser during the original extradition proceedings by “concealing” the fact that Assange had fathered two children during his time in the Ecuadorian embassy until March 2020, when he “chose to deploy that information in support of his bail application”.

Edward Fitzgerald QC, representing Assange, told the court the district judge was in the best position to assess it and reach her decision having heard the evidence.

He said Professor Kopelman’s report, in which he did not reveal the true nature of Assange’s relationship with Ms Moris, was given long before any court hearing and against a background of concern for the “human predicament” in which Ms Moris found herself at the time.

The barrister said this included fears for her safety and that of the couple’s two children, after a surveillance organisation had taken DNA from their baby’s nappy, then turned its attention to Ms Moris and plotted to kidnap or poison Assange.

Lord Justice Holroyde, sitting with Mrs Justice Farbey, gave the US the go-ahead to argue all five parts of its appeal at the main hearing later this year.

The judge found Judge Baraitser had attached too much weight to the evidence of Professor Kopelman, adding it was “very unusual” for an appeal court to have to consider evidence of an expert, which has been accepted by a lower court, who has been found to have misled the court.

He added: “Given the importance to the administration of justice of a court being able to reply on the impartiality of an expert witness, it is in my view arguable that more detailed and critical consideration should have been given to why (the professor’s) ‘understandable human response’ gave rise to a misleading report.”

Both sides will now prepare for the full appeal, which will be heard in person on October 27 and 28.

If Assange is extradited, the US has said it would consent to him being transferred to Australia to serve any prison sentence he may be given.