The WikiLeaks founder, Julian Assange, has lost a high court battle to prevent the US government expanding the grounds for its appeal against an earlier refusal to allow his extradition to face charges of espionage and hacking government computers.

On Wednesday, judges said a report from Assange’s psychiatric expert that was submitted at the original hearing in January could form part of Washington’s full appeal in October.

Sitting in London, Lord Justice Holroyde said he believed it was arguable that the evidence given by Prof Michael Kopelman should have had less weight attributed to it when the original decision was made.