Chilean exiles are holding an overnight vigil in London in advance of a decision by Britain's highest court on whether their former leader, Augusto Pinochet, is immune from arrest and extradition.

Five senior judges will rule on Wednesday 1400 on whether to uphold a High Court decision that General Pinochet is immune because the crimes he's accused of were committed when he was head of state.

If the judges are divided, as unconfirmed reports say they are, the majority will prevail.

The BBC diplomatic correspondent says that whichever way the ruling goes, bitterness between supporters and opponents of Generel Pinochet in Chile could boil over.

He says human rights organisations have argued that there can be no immunity under international law for crimes against humanity, and that a ruling to allow extradition would mark another step towards universal jurisdiction.