In a test case that will have international ramifications, five Law Lords are being asked to overturn last week's High Court ruling, which gave General Pinochet immunity from prosecution on charges of genocide and terrorism.
The Law Lords agreed to listen to new evidence and rule formally on its admissibility later. General Pinochet's legal team had argued strenuously that the Lords should not open themselves to such new evidence, but restrict themselves to the evidence given before the High Court last week.
Alun Jones QC, appearing on behalf of the Crown Prosecution Service and Spanish authorities seeking General Pinochet's extradition, made an apeal to the five Law Lords, asking them to "decisively reject the repugnant notion, offensive to all notions of human rights and individual responsibility for crimes against humanity, painstakingly devel- oped in international law in the 20th century, that a person has immunity from such crimes committed in the course of official functions as head of state".
Mr Jones maintained that General Pinochet would be culpable for crimes against humanity, including the killing of children, torture and kidnapping. He was responsible for them as head of state, as these were not defensible functions of a national leader.
The CPS and Spanish authorities also assert that General Pinochet was not officially in power when some of the atrocities took place, and thus cannot claim immunity as head of state.
After the military coup led by General Pinochet on 11 September 1973, a decree was issued legitimising the overthrow of the democratically elected left-wing government of President Salvador Allende. But by then at least 28 people had disappeared, believed to be murdered. Allende himself was one of the victims.
Mr Jones told the Lords that General Pinochet's regime had organised the dreaded secret police force, Dina, which developed programmes of "disappearance, torture, and executions". A successor to Dina, the National Centre for Information, continued the terror, said Mr Jones. "It recommenced with even more severe repression. The system was widespread and universal with no deference to age ... or gender, but was particularly intense towards certain groups such as Jews and the Callaqui Native Community."
New torture centres were set up "to create a more effective and systematic programme of terror" and "this programme was presided over by Pinochet himself".
Mr Jones told Lords Steyn, Lloyd, Slynn, Nicholls and Hoffman that under international law "the general principle is that individual responsibility applies whoever you are, even if you are head of state".
In a highly unusual move, the Law Lords agreed to hear depositions from former torture victims, including the British doctor Sheila Cassidy and the family of a fellow Briton, William Beausire, as well as Amnesty International and the Medical Foundation for the Care of Victims of Torture.
The hearing continues today.