The former Chilean military leader, General Augusto Pinochet, was arrested in London on 17 October on a warrant from Spain, which wants to try the general for the deaths of Spanish citizens during his years of power in Chile between 1973 and 1990.

General Pinochet: The Chilean Government is ready with his defence

On 28 October the UK's High Court decided that General Pinochet had immunity from prosecution. The Spanish Government is appealing against that ruling.

Each of the five Law Lords will announce on Wednesday whether he would allow or dismiss the appeal. There is then a formal vote, and the Law Lords will reach their decision - if necessary by a majority of four to one or even three to two.

Outcome unclear either way

If the Law Lords dismiss the appeal, it means they agree General Pinochet is immune from prosecution. That would mean his arrest was unlawful.

He would be free to leave the UK immediately. The British Government would not become involved in the case. It would have been entirely a matter for the courts.

But even if the Law Lords allow the appeal, it does not mean that Spain's application for extradition would necessarily be granted. However, General Pinochet would have to remain in England while the legal process continued. He is currently on bail, and could be moved from the Grovelands Priory Hospital in London if the police agreed.

If the appeal is granted, Home Secretary Jack Straw will have to decide whether to let the case go any further. He would have up to a week in which to make up his mind; a magistrate has said Mr Straw would have to decide by 2 December whether to issue what's called an 'authority to proceed', listing the charges against General Pinochet. That time limit could be extended.

According to reports from Santiago, the Chilean Government is preparing a detailed diplomatic memorandum, repeating some of the legal arguments put to the courts on behalf of General Pinochet.

Home Secretary Jack Straw would decide whether to let the appeal go further

If necessary, Chile would submit these arguments to Mr Straw on Thursday, and it would then be up to the Home Secretary to decide whether to issue an authority to proceed. If he decided not to, he would then have to cancel the arrest warrant under which General Pinochet is being held and order his release from custody.

If Mr Straw gave his authority for the case to proceed, General Pinochet would have to appear before a Magistrate in London on 2 December unless he was considered too ill to do so.

The extradition proceedings would then continue. Even if the courts decided that General Pinochet should be extradited to Spain, the Home Secretary might still decide at the end of the proceedings that he should not be handed over for trial.