Mr Straw has until Friday to rule on whether the extradition process against General Augusto Pinochet can go ahead but it is thought he may announce his decision on Wednesday

The government has refused to speculate on when the decision will be made but Legal Affairs Correspondent Joshua Rozenberg says Amnesty's lawyers are simply trying to buy time.

Joshua Rozenberg: "This could all happen very quickly"

He says: "They are worried that if the announcement goes the way Amnesty International does not want it is possible there won't be time [to obtain an injunction].

"What they are trying to find out is whether they have got any right to be heard because they are not strictly speaking to a party to this case."

Jack Straw's decision must be made by Friday

Mr Straw must rule on whether to grant an extradition request by Spain, which wants to try the 83-year-old general on charges of murder and genocide. His deliberations follow a ruling in the UK's highest court, the House of Lords, that General Pinochet does not have immunity from such a request.

An opinion poll, conducted by ICM for The Guardian newspaper, has found the UK split on the future of General Pinochet.

Some 36% of those polled said he should be allowed to return to Chile while 34% were keen on him being extradited to stand trial in Spain and 30% were undecided.

Michael Mansfield: Urging Mr Straw to extradite General Pinochet

But there is more partisan pressure from a full-page advertisement in The Independent newspaper, which urges Mr Straw to "allow the full legal process of the extradition" of General Pinochet.

The advert was paid for by more than 300 signatories, including actresses Emma Thompson and Juliet Stevenson, musicians Billy Bragg and Peter Gabriel, playwright Harold Pinter and lawyer Michael Mansfield, QC.

Amnesty International spokesman Neil Durkin on the High Court appeal

Both the human rights group Amnesty International and General Pinochet's lawyers have pleaded in vain with the Home Secretary to be allowed advance notice of his decision.

His lawyer, Michael Caplan, told BBC News Online: "It's difficult to say exactly what is going to happen. It's really a case of wait and see but it's open to either side to apply for judicial review of his decision."

General Pinochet: Amnesty campaigned for extradition

If Mr Straw rules in General Pinochet's favour it is likely to spur a mad dash to lodge an appeal.

The Chilean Government is expected to spirit him away from his mansion at Wentworth, in Surrey, to a waiting aircraft at RAF Brize Norton in Oxfordshire as soon as possible.

But lawyers for the Crown Prosecution Service, representing the Spanish Government, would head straight for the High Court in a bid to get a stay of proceedings pending a full judicial review of Mr Straw's ruling.

Liz Mackean reports from Madrid on Spaniards' view of General Pinochet

The Chilean aircraft will not be able to take off without the permission of the RAF, which will wait for the nod from the High Court before allowing it to do so.

If Mr Straw does agree to extradition he is likely to spark off more huge demonstrations in Chile, where British Embassy officials are keeping a low profile.

Such a decision, which must be made by Friday, is also likely to be challenged by General Pinochet's lawyers.

They may well raise the subject of Lord Hoffmann, the Law Lord whose vote won the day for supporters of the extradition process, who is a director of a charity linked to Amnesty International.