The BBC's Jane Peel: "The extradition charges have once again brought the crowds out"

Police kept supporters and opponents of the former dictator apart as proceedings got under way at Bow Street Magistrates' Court in London.

Gen Pinochet is wanted by Spain for a string of human rights crimes during his 1973-90 rule.

The 83-year-old was arrested in Britain on 16 October last year, while recovering from back surgery at a London clinic, and has been fighting extradition ever since.

Gen Pinochet will face 35 charges, mainly allegations of torture, which will be detailed in the opening session. They are the result of an investigation by a Spanish judge, Baltasar Garzon.

Deteriorating health

Gen Pinochet's supporters, who were in the majority outside the courtroom, say his health his deteriorating and they fear he may die before the case is resolved.

Pro-Pinochet demonstrators make themselves heard

But Reed Brody, Advocacy Director of Human Rights Watch, said: "Pinochet's victims have waited 25 years for this historic moment.

"For the Crown prosecutors to formally read out the charges of torture and conspiracy against General Pinochet is a measure of vindication for the thousands who were killed, tortured or disappeared by his regime."

But one of Gen Pinochet's prominent supporters, businessman Peter Schaad, said: "It's most ironic that Spain, the alma mater of fascism should ask for the extradition of Pinochet.

"I don't understand why Judge Garzon doesn't concentrate on the million or so people who died for political reasons in his own country.

Gen Piochet's health is thought to be rapidly deteriorating

"Spain needs people like Garzon like a hole in the head."

The hearing, expected to last about five days, will then be taken up with complex arguments on extradition law, notably the European Convention on Extradition, to which Britain and Spain are parties.

Deputy Chief Magistrate Ronald Bartle will decide whether the charges against Pinochet are extraditable crimes, whether Spain has jurisdiction and whether the legal paperwork is in order.

Gen Pinochet will not attend the hearing, but must be present for Mr Bartle's judgment, which is expected to be given long after the hearing.

The BBC's James Reynolds reports from Chile: "The debate about the past has re-opened"

Even if Mr Bartle approves the extradition, Pinochet's lawyers still have various legal options, which could take months - if not years.

Home Secretary Jack Straw may then approve the extradition request, or reject it on grounds such as health and age.

The final stage could be an application for judicial review of Mr Straw's decision.

Chile's foreign minister Juan Gabriel Valdes said he feared a "fatal outcome" as the general's health was unlikely to withstand a legal battle that could still take more than two years.

Mr Valdes' remarks came after a UK newspaper reported that Gen Pinochet had suffered a stroke which has left him bedridden for more than two weeks.

He is known to wear a heart pacemaker and has suffered from diabetes and a range of other ailments.

On Sunday the Home Office rejected claims by former Chancellor Lord Lamont, a supporter of Gen Pinochet, that the government is considering a deal to send the general back to Chile.

Lord Lamont had said the government may release the general on humanitarian grounds, if his lawyers agree not to press ahead with their appeal against his extradition to Spain.

But a Home Office spokesman insisted that the government is leaving the matter to the courts for the moment.

He said: "There is no deal. The home secretary cannot intervene at this stage as the matter is before the courts.

"The home secretary's role is at the end of the process."