Mr Straw has decided to allow Spain permission to go ahead with an extradition request against the 83-year-old general.

Mr Straw said he had considered Britain's national interest, General Pinochet's age and health but decided they were not reasons enough for rejecting the extradition request.

General Pinochet faces allegations of torture from his last two years in power between 1988 and 1990.

Helen Callaghan: No certainty that Pinochet will be extradited

British judges drastically reduced the number of charges he could face after deciding allegations of torture abroad were not covered by UK law before it adopted an international torture convention in December 1988.

But Mr Straw's decision does not mean that the general, who was made a life senator in Chile after he stepped down as president in 1990, will be extradited to Spain immediately.

Sovereign immunity

He is expected to fight extradition through the British courts, which could take several years.

The BBC's Legal Affairs correspondent Joshua Rozenberg: "This could drag on for years"

Former Tory Home Secretary Kenneth Clarke said Mr Straw had made a "bad decision".

He said: "It's bad for the democratic settlement in Chile and it's bad for our relations with Chile, which is a friend of Britain."

Kenneth Clarke: "Jack should have exercised his discretion in the national interest"

Mr Clarke said it was ironic that Mr Straw was releasing IRA convicts, such as the Balcombe Street gang, to accommodate a political settlement in Northern Ireland while his actions in the Pinochet case could unravel the political settlement which had been reached in Chile.

'Reopening old wounds'

Mr Clarke said if General Pinochet was put on trial it would "reopen old wounds" in Chile.

But Amnesty International spokesman Brendan Paddy said Mr Clarke's argument was "utterly flawed".

He said: "The people he is talking about have faced trial and have, in most cases, served lengthy sentences.

"General Pinochet has been given complete immunity, and immunity has never been on offer to the IRA."

The complex legal saga began last October with the general's arrest in London. British police were responding to a request by three Spanish judges investigating charges of torture and genocide against Spanish citizens during the former dictator's 1973-1990 rule in Chile.

No legal precedent

The groundbreaking case had no precedent in British law and was eventually passed to the UK's highest court, the Law Lords, for judgement.

Lawyers for General Pinochet have consistently argued he enjoyed sovereign immunity against any alleged crimes committed as head of state.

Last December, a panel of five Law Lords found by a vote of 3-2 that the former dictator did not enjoy sovereign immunity and shortly afterwards Mr Straw issued an Authority to Proceed in legal action to extradite the general.

Charges much reduced

But the decision was set aside and the case returned to the Law Lords after it was found that one of the original judges, Lord Hoffmann, had failed to declare links to the human rights group Amnesty International.

The BBC's James Reynolds reports on how the decision is likely to be greeted in Chile

It was decided his link to Amnesty represented a significant conflict of interest. The organisation gave evidence to the Lords during their deliberations and has been pressing for General Pinochet to face trial.

A second panel of seven Law Lords was convened, which last month also decided General Pinochet could face extradition proceedings, but for a significantly reduced set of charges.

In a highly complex ruling, they decided that he could only be tried on two of the original 32 charges which were allegedly committed before the 1988 adoption of the international torture convention in December 1988.

General Pinochet has been under house arrest at a rented home in Wentworth, Surrey, pending the outcome of the extradition saga.

On Thursday the extradition case against General Pinochet at Bow Street magistrates' court in central London was adjourned until 30 April.

A magistrate granted a request by General Pinochet's solicitor Michael Caplan for the adjournment while his lawyers study the Home Secretary's decision to issue an Authority to Proceed in the case.