This is a 1998 case.
Senator Augusto Pinochet-Ugarte came to the the United Kingdom for medical treatment. He was greeted by diplomats at the airport because he was a former Chilean President.
A few days later Senator Pinochet was arrested. A Spanish judge Baltasar Garzon had issued an arrest warrant
The House of Lords decided that Pinochet could be extradited to Spain. There was no sovereign immunity for a former head of state. The commission of crime is not a legitimate function of a head of state.
In R v Bown Street Metropolitan … (ex Parte Pinochet Ugarte) Number 2.
Then the Lords overturned its ruling because one of the law lords was married to someone who had agitated for Pinochet’s extradition. That was Lord Hoffman.
Pinochet Number 3 was a case that reaffirmed that the senator for life did not benefit from state immunity. But he could only be prosecuted for crimes allegedly committed after 1988 when a certain act was passed.