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LONDON (Reuters) - Chile signed away any rights former dictator Augusto Pinochet might have had to claim immunity from prosecution abroad for torture 11 years ago, a lawyer acting for Spain told Britain's top court on Tuesday.

Alun Jones said torture had been forbidden by Chile's constitution since 1925, and in 1988, with Pinochet still president, it had ratified the International Convention on Torture which made it an offense under international law.

"That should act as an inhibition on Chile arguing that 'Torture is a matter for us. It happened in our state. It was in the exercise of government authority'," he told a seven-strong panel of senior judges in the House of Lords.

"They have signed up to the convention which says 'Forget about all that. It is international. It is internationally punishable'."

The Lords are rehearing the question of whether, as a former head of state, Pinochet has immunity from prosecution for murder, torture and hostage-taking, and therefore whether an application by Spain for his extradition can proceed.

In November, a panel of five law lords ruled by three to two that 83-year-old Pinochet did not have immunity.

But the judgment was set aside after it emerged that one of the five, Lord Hoffmann, chaired the charity arm of Amnesty International. The human rights watchdog had been allowed to make legal submissions to the court.

Jones's case took the whole of the first day of the rehearing on Monday, and he continued it in a 2-1/2 hour session of the court on Tuesday before a lunch break.

On Monday, Jones said Spain claimed that Pinochet led a conspiracy to torture thousands of Chilean and other nationals after, and just before, seizing power in Santiago from Salvador Allende in September, 1973.

He said the methods used had been "the most hideous imaginable," including rape, crushing of bones and the use of dogs to assault victims sexually.

On Tuesday, Jones said that in one case the mother of a subject of torture was stripped naked and forced to watch as his guards pretended to shoot him.

"It is inconceivable that the international community, in framing this convention, intended to exclude people at the highest rung of government...but to include in liability public officials who were accepting orders," he added.

Earlier, Lord Browne-Wilkinson, who presides over the seven-judge panel, said the group had decided overnight it would be desirable to ask Britain's Foreign Office when it regarded Pinochet as having become head of state. "It might or might not be vital, but it would be helpful," he said.

Lawyers for Pinochet claim he took over as head of state immediately the coup against Allende succeeded. The Chilean embassy in London wrote to the court overnight to back up this claim and clarify evidence it had submitted earlier.

Jones argued on Monday Pinochet was not appointed to the post until, at the earliest, June 1974, and that the Chilean evidence confirmed this.

He said Pinochet therefore could not have had immunity in respect of the spate of torture which occurred in the months after the coup.

If the judges rule in Pinochet's favor following a hearing now expected to last more than a week, he is expected to return home on a Chilean air force plane which is already waiting at a military airport outside London.

But if they rule against him, he could be forced to remain under police supervision at a mansion in the countryside west of London for months as the process to extradite him makes its way through the courts.