Wikileaks founder Julian Assange has started his latest legal action to try to block his extradition to Sweden at the Supreme Court in London, BBC reports.
The appeal is based on whether the Swedish prosecutor who issued the European Arrest Warrant against him had the judicial authority to do so.
Mr Assange is wanted by the Swedish authorities for questioning over alleged sex offences, which he denies.
Judgement is expected to be reserved to a later date.
The key legal question for the seven judges is whether the prosecutor who issued the arrest warrant had the judicial authority to do so under provisions of the 2003 Extradition Act.
Mr Assange's lawyer, Dinah Rose QC, said it was "a matter of fundamental legal principle" that the person issuing such a warrant was both independent and impartial.
But she said the Swedish prosecutor was a party in the Assange case and therefore was not either of these things.
