The former dictator is currently under house arrest in Britain, fighting a extradition request from Spain, where he is wanted to stand trial for human rights abuses.

The House of Lords is expected to make a decision about extradition in September.

Relatives of the "disappeared" have campaigned to bring Pinochet to trial

But reports have emerged that secret negotiations took place between the foreign minister of Chile, Gabriel Valdes, and his Spanish counterpart, Abel Matutes, to try to halt the extradition to Spain.

Chile hopes to persuade Spain to accept the alternative of international arbitration, which could involve the International Court of Justice in The Hague. This would mean an early return to Chile for the 83-year-old former leader.

Reaction in Spain to the reports was swift and angry. Legal organisations said anything other than the full trial in a court of law would undermine democratic institutions in Spain.

Chile's Foreign Minister, Juan Gabriel Valdes: "What we are seeking is a solution"

Santiago Martinez, president of the Professional Association of the Magistracy, the country's largest judicial association, told El País: "If [the government ] is following the judicial route, only the courts can finish that route, and no recommendation from the government can influence it."

The Judges for Democracy association in Spain also warned that arbitration in this case would be against the Spanish constitution.

Spokeswoman Montserrat Comas said that such a way out would only be appropriate "when there is a political conflict between countries, and not when one emerges from the fulfilment of judicial procedures".

But Chile said every stage of the government's dealing with Spain had been well documented and that no "secret" negotiations had occurred.

The BBC's Daniel Schweimler: "The reaction in Spain has been swift and angry"

It said that since April it discussed the idea of international arbitration to see whether Spain or Chile has the better right to determine what happens to Gen Pinochet.

A correspondent in Santiago says on 23 July, Mr Valdes requested arbitration in a letter to Mr Matutes.

If Spain drops the extradition request, there are only two things that could stop Gen Pinochet from leaving the UK. The first is if another country immediately submits an extradition request. The second is the unlikely event of a decision to prosecute him there.

But a number of other countries have issued or are considering issuing extradition warrants but the Spanish warrant takes precedence.

Carlos Reyes, of the London-based anti-Pinochet group Chile Democratico, said he was disturbed by the reports.

"The current spectacle of politicians desperately manoeuvring to prevent the bringing of justice of Pinochet is of great concern to all those who suffered under his regime," said Mr Reyes.

The UK Home Office has confirmed that if Spain dropped its extradition request, the general, who has been detained in the UK for the past 10 months, would be free to leave.

Charges brought against Gen Pinochet, have been an embarrassment for the Popular Party government of Spanish Prime Minister Jose Maria Aznar.

Spain is the biggest foreign investor in Chile and tens of thousands of Spaniards live in the country.

Amnesty International has argued that there is no real prospect of Gen Pinochet being tried in Chile or by an international tribunal.

It said extradition to Spain was the only means by which Gen Pinochet could be deprived of a "wall of impunity".