WHAT STARTED with another routine shopping trip to London for General Augusto Pinochet suddenly began to go horribly wrong. On 16 October, as he lay recovering from a minor back operation, the former Chilean dictator received a visit from Scotland Yard. He was under arrest because of an extradition request from Spain on charges of mass murder, torture and kidnapping.

Thus began a saga with extraordinary twists, passion and pathos. What had happened in Chile 25 years ago has led in Britain to a fierce debate, pushing aside the politics of the centre and bringing back the old divisions between left and right.

In the immediate aftermath of the arrest, Peter Mandelson became the unlikely hero of the left by saying it was "gut wrenching" that "such a brutal dictator" should be claiming diplomatic immunity. This was, however, the first and last public cry from the radical past of New Labour. From now on the party line was that it was a purely legal matter.

Past and present Conservative politicians, on the other hand, were outraged. Baroness Thatcher demanded that General Pinochet be freed at once. William Hague and his front bench, after a bout of initial dithering, took up the cry.

There was apprehension in Washington that an open trial could lead to a public airing of the CIA's role in the Pinochet coup.

The legal process began with the High Court ruling in favour of immunity but then the House of Lords voted by three to two that the former dictator should face justice. Then thatdecision was overturned because Lord Hoffmann had failed to disclose his links with Amnesty International.

So legally we are now almost back to square one. But it would be wrong to think nothing had changed. Jack Straw resisted great pressure and refused to free the general, becoming a second unlikely hero of the left. According to opinion polls, his decision to let the legal process continue has been popular.

General Pinochet's opponents are exploring other legal avenues, including the possibility of trying him for torture under the Criminal Justice Act. And there is nothing to say the next panel of the lords will not also rule against him. The one salient lesson of the Pinochet affair is to expect the unexpected.