Ronald Bartle, the magistrate assigned to the Pinochet case, has to decide whether General Pinochet should be committed to await a decision from the Home Secretary on his extradition.

For this reason, the proceedings at Bow Street Magistrates' Court are known as "committal" proceedings. Mr Bartle is expected to announce his decision on 8 October.

General Pinochet has been excused appearing at the next hearing after a court heard he had recently suffered two minor strokes.

He was due to attend to hear whether he would be committed to face extradition.

The case is not like an ordinary criminal prosecution. The magistrate does not have to decide whether there is enough evidence to justify putting General Pinochet on trial. Because both Spain and the United Kingdom have both signed the European Convention on Extradition, all Mr Bartle has to do is to decide whether the former dictator stands accused of what is called an 'extradition crime'.

The BBC's Helen Sawyer: "His lawyers will argue that he should be set free"

In April 1999 the Home Secretary Jack Straw said he considered that General Pinochet was accused, in Spain, of two extradition crimes - torture and conspiracy to torture. Mr Straw gave the necessary authority for the extradition case to proceed on this basis.

It was the second time Mr Straw had issued what is called an authority to proceed. The Home Secretary took account of a ruling from the law lords in March 1999. That said the only offences on which General Pinochet could be extradited were those alleged to have taken place after 8 December 1988, when the an international agreement on torture became binding on Spain.

It was the second time the law lords had ruled on the question of whether the former dictator had immunity from extradition as a former head of state. The first ruling was set aside because one of the judges, Lord Hoffmann, had taken part in the case while disqualified. He had close links with Amnesty International, a party to the case.

Pinochet faces charges of human rights crimes if extradited

So the magistrate, Mr Bartle, will have to decide whether General Pinochet is accused of committing torture or conspiracy to torture after 8 December 1988.

That question is not as simple as it looks. At the time Jack Straw gave his authority for the case to proceed, the only extradition crimes facing General Pinochet were one charge alleging torture on 24 June 1989 and a handful of conspiracy charges relating to the period after 1988.

Since then, the Spanish prosecuting judge has put forward another 36 or so allegations of torture or conspiracy which are said to have taken place after 1988. Lawyers for the Spanish government are expected argue to that General Pinochet could be extradited on these charges as well.

General Pinochet's lawyers will tell the magistrate that the only charges on which he can be committed for extradition are those notified by Spain by the time Mr Straw gave his authority for the case to proceed.

Spanish judge Baltasar Garzon: seeking Pinochet's extradition

The general's lawyers will also argue that conspiracy is a continuing act. As a result, they'll say the magistrate must disregard any allegations of conspiracy to torture that began before December 1988, even if they continued after that date. That would leave the General facing just one just charge of torture.

Another question for the magistrate may be whether Spain has jurisdiction to put General Pinochet on trial for torture.

The international torture convention allows Spain to try someone for torture if the accused person is Spanish; or the alleged torture took place in Spain; or the alleged victim is Spanish.

The first two conditions do not apply in this case. That leaves the question of whether any of the people who faced or suffered torture after 1988 were Spanish.

The case has sparked protests across the world

General Pinochet's lawyers say there is no evidence that they were. Spain is expected to argue that it does have jurisdiction to try General Pinochet and, in any case, jurisdiction is not an issue for Mr Bartle to deal with.

If the magistrate decides not to commit General Pinochet, lawyers for the Spanish government may go to the High Court and argue that Mr Bartle got the law wrong.

Other countries such as France or Sweden might begin extradition proceedings against him. Or, if there is enough evidence, he could be arrested and charged with torture under English law. Otherwise, he would be free to return to Chile.

On the other hand, Mr Bartle may make an order to commit. In that case General Pinochet's lawyers would be left with two options.

They would be able to challenge the magistrate's decision in the High Court by applying for habeas corpus. If they made an application within 15 days, the general would be able to stay here until the case was finally decided.

Jack Straw gave authority for the case to proceed

If the High Court refused to grant habeas corpus, General Pinochet could appeal to the House of Lords. That could take several months. If General Pinochet lost, the case would go back to Jack Straw for a decision.

On the other hand, they could decide not to apply for habeas corpus. If that happened, the case would go straight to Mr Straw.

The home secretary would then consider the case afresh. It is only at this stage that he would consider medical reports. Mr Straw is not allowed to send General Pinochet for trial in Spain if he thinks it would be unjust or oppressive to do so.

So if Mr Bartle rules against General Pinochet, his lawyers will look carefully at both the reasons for the magistrate's decision and the state of their client's health. If they think they have strong grounds for an appeal to the courts, they may continue down the legal road.

If there are indications that Mr Straw might be willing to free General Pinochet on medical grounds, there would be no reason to spend any more time or money on further legal challenges.