Dining at his favourite restaurant in Cannes, the former Haiti president Jean Claude "Baby Doc" Duvalier may well feel aggrieved at this change of rules, as might General Idi Amin of Uganda, living in Jeddah on a Saudi stipend. Those still in power, such as Laurent Kabila in the Congo and Kim Jong Il in North Korea, will also know that they may be held to account in the future for what they do now.
The lords' ruling that, in the Pinochet case, the 1988 Torture Act is not retrospective is a blow to the prospect of extraditing him to Spain. However, legal experts say the ruling establishes that former heads of state cannot claim blanket immunity.
The concept of state immunity was enshrined in England in the State Immunity Act of 1978, for diplomatic reasons. But the concept had been challenged after the First World War when there was an unsuccessful attempt to bring charges against Kaiser Wilhelm II.
After the Second World War, the prosecution of Nazi war criminals was firmer. The Charter of the International Military Tribunal in 1945 said: "The official position of defendants, whether heads of state or... officials in government departments, shall not be considered as freeing them from responsibility or mitigating punishment."
Since then there have been international tribunals set up for war crimes committed in Rwanda and former Yugoslavia, again reiterating that those accused of human rights offences should not be allowed to hide under the cloak of state immunity.
The tide of law appear to be running against the dictators. The Rome statute for the International Criminal Court, signed by 120 countries including the United Kingdom, Chile and Spain, though not yet ratified, states: "In particular, official capacity as a head of state or government, a member of a government or parliament... shall in no case exempt a person from criminal responsibility under this Statute."Reuse content