Julian Assange’s battle against his extradition to the United States could be heading to the Supreme Court after the High Court today certified a point of law of general public importance over assurances given by a requesting state.

Assange, 50, is wanted on 18 counts over WikiLeaks’ publication of leaked military documents relating to the US wars in Afghanistan and Iraq a decade ago.

He has been held in the high-security HMP Belmarsh in south east London since 2019 after he was arrested and removed from the Ecuadorian embassy, where he had stayed since 2012.

District judge Vanessa Baraitser ruled that Assange should not be sent to the US as his mental health was ‘such that it would be oppressive to extradite him’.

However, last month, the High Court found that assurances given to the UK government about the conditions in which Assange would be held were ‘sufficient to meet the concerns which led to the district judge’s decision’.

Assange sought to appeal to the Supreme Court, which will now have to decide whether to grant the WikiLeaks founder permission to take his case to the UK’s highest court.

The lord chief justice Lord Burnett and Lord Justice Holroyde certified ‘a single point of law, namely in what circumstances can an appellate court receive assurances from a requesting state which were not before the court of first instance in extradition proceedings’.

Burnett added: ‘We refuse leave to appeal. The Supreme Court will itself consider any application for such leave.’

In brief written reasons for their decision, the judges said that ‘although the law in this jurisdiction has long been settled, it does not appear that the Supreme Court has considered the question’ of assurances, which are ‘at the heart of many extradition proceedings’.

Assange has also previously indicated that he intends to challenge the district judge’s decisions on the issues which were decided against him.

Speaking outside the Royal Courts of Justice in London, Assange’s fiancée Stella Moris said the decision was ‘precisely what we wanted to happen’. She added: ‘Our fight goes on and we will fight this until Julian is free.’