Besides its immediate effect on General Pinochet, the ruling of the House of Lords has more far-reaching implications.

Human rights campaigners hope it will help deter people in power around the world from committing atrocities, and give a push to efforts to establish a universal jurisdiction for crimes against humanity.

The Law Lords decided first that the English courts did have jurisdiction to try crimes of torture and hostage-taking covered by international conventions.

They then ruled that crimes against humanity could not be considered part of the normal functions of a head of state, so no immunity could be claimed for them.

Even Clinton could be at risk

Legal experts say the implications are potentially very serious.

Any former head of state or high official who travels outside their own country is liable to be arrested on the basis of a request for extradition from some third state, according to the precedent set by this ruling.

"I think that might cause serious reconsideration of immediate travel plans of quite a large number of people," said Jeremy Carver, head of International Law at the London-based firm Clifford Chance.

Presidents have many enemies

On this analysis, even President Clinton once he leaves office might be vulnerable to prosecution for ordering missile attacks on Afghanistan.

More probably, human rights campaigners hope the Lords ruling will give a push to efforts to try crimes against humanity in a permanent International Criminal Court.

But according to Amnesty International that won't be able to deal with the Pinochet case, because it would not have retrospective authority.

"The International Criminal Court, though, is a major step forward because it does set up an institution which will have that deterrent effect for future crimes of this nature," said David Bull, director of Amnesty's British section.

Legal experts are only beginning to assess the huge implications of the Lords judgement for international law.