Speaking in a Lords debate, the former prime minister told peers there was "widespread suspicion" of collusion between the British and Spanish authorities before he was detained. General Pinochet is facing extradition to Spain on charges of torture and murder.
Lady Thatcher claimed he was arrested on the basis of an unlawful warrant and had been illegally held for six days under that warrant. The former prime minister, who was making her first speech in the Lords for more than three years, has visited Senator Pinochet twice since his arrest.
She has protested at the manner of the arrest and the continuing detention of a man she has described as a long-standing friend of Britain.
In a debate initiated by Lord Lamont of Lerwick, the former Tory chancellor, Lady Thatcher said the case had sullied Britain's reputation. "Senator Pinochet is, of course, being victimised because the organised international left are bent on revenge," she said. "But on his fate depends much else besides. Henceforth, all former heads of government are potentially at risk."
Lord Lamont also challenged ministers as to whether there had been collusion with Spain over the affair. He said that 83-year-old General Pinochet was "still under anaesthetic" after his operation when he was arrested by "armed police"and the arrest had been "roundly condemned" by Chile's government which included opponents of the General. He urged the Home Secretary Jack Straw to "take steps to free a man who is a political prisoner in this country".
Lord Howe of Aberavon, who was Foreign Secretary under Lady Thatcher but later became one of the chief instigators of her downfall, said Mr Straw had failed to consider the "hazards and dangers" of trying to intervene in the "finely balanced" peace and reconciliation process in Chile. And he warned: "I hesitate to think of the consequences if he should die in our custody. Someone, who others seek to present as a monster, will become a martyr."
Lord Clinton-Davis, the former Labour minister, accused Lord Lamont of making an "extraordinarily ill-advised" speech. Peers had been warned at the beginning of the debate by the Government Chief Whip, Lord Carter, that the issue was sub judice and Lord Clinton-Davis said Lord Lamont had "brought into questions" matters which would be dealt with by the courts. "It is vital in a democracy to respect those tenets of law so flagrantly violated by him tonight."
Viscount Cranborne, the former leader of the Conservatives in the Lords, accused the Government of "a desire to make obeisance to the political gods that they worshipped at university in the Sixties".
Lord Williams of Mostyn, the Home Office minister, defended Mr Straw's actions and condemned many of the claims that had been made in the debate by Tory peers as "unworthy and ignoble" and "wrong".
He assured the House that the actions of the Home Secretary, the police and the Crown Prosecution Service had been in accordance with the 1989 Extradition Act, passed at a time when Lady Thatcher, Lord Howe and Lord Lamont were in government.
"This has nothing to do with legal devices introduced by the present Government," he said. "The Home Secretary has behaved properly, without fear or favour of criticism from left or right, without any political contact with his colleagues in government. I know that, for myself, to be true."Reuse content