Baroness Thatcher called for the immediate release of former Chilean dictator General Augusto Pinochet last night, saying he had saved many British lives during the Falklands War.
Lady Thatcher, who was Prime Minister during the 1982 war with Argentina, said Chile had been "a good friend to this country" during the conflict and must now be released from detention.
"General Pinochet must be allowed to return to his own country forthwith," she wrote in a letter in today's Times.
Lady Thatcher, who invited the general for drinks two weeks ago, just before he went into a London clinic for a back operation, warned against interfering in what she said was an "internal matter" for Chile.
Her attitude is in stark contrast to that of the Prime Minister, Mr Blair, who also stepped into the dispute last night.
Mr Blair stressed that Britain had not been acting for political reasons by carrying out the arrest.
He insisted that the detention came in response to an extradition request from Spain. It was not the result of the Government's ethical foreign policy.
Chilean members of parliament warned that General Pinochet was in "extremely delicate" health and that if his condition deteriorated under continued detention, it could ignite fresh unrest in Chile.
The general, under police guard in a private London hospital, faces possible extradition to Spain over allegations of mass murder following his bloody coup in 1973, as well as calls for him to be prosecuted in Britain.
The embassy says its relationship with Latin American governments was "sufficiently robust" to withstand scrutiny of its role in the coup that brought the former dictator to power in 1973.
Mr Tom Bradtke, the embassy's deputy chief of mission, said Gen Pinochet's case "is not an issue we are involved in."
A second meeting between Chile's ambassador to Britain, Mr Mario Artaza, and the Foreign Office director for the Americas, Mr Peter Westmacott, yesterday failed to persuade London that Gen Pinochet could claim diplomatic immunity.
The all-party Parliamentary Human Rights Group has supported a call by Amnesty International for the Metropolitan Police to investigate the cases of four British citizens who were tortured during the Pinochet regime.
The group representing Chilean exiles and victims, Chile Democratico, said yesterday that it would be ready to present legal papers for a private prosecution of the general next Wednesday.