JULIAN Assange's current court appearance in Britain has nothing to do with sex or United States diplomatic cables or even with WikiLeaks. But it may make an important contribution to European law.

The United Kingdom Supreme Court will be considering the point I raised on his behalf when a Swedish prosecutor claimed to be a ''judicial authority'' empowered to issue a warrant to have him extradited to prison in Stockholm. My written argument began quite bluntly: ''The notion that a prosecutor is a 'judicial authority' is a contradiction in terms.''

Judges must, as their defining quality, be independent of government. Police and prosecutors employed and promoted by the state obviously cannot be perceived as impartial if they are permitted to decide issues on the liberty of individuals.

They are expected to be zealous in working up evidence against a suspect, so they are the last people who can be trusted to weigh up impartially the evidence they themselves have drummed up. That is a matter for a court.

So how comes it that in Sweden and many other European countries, prosecutors and even policemen and women are allowed to issue a so-called European arrest warrant, which has the draconian effect of requiring the arrest of people in another country and dragging them for trial in the state which has issued the warrant?