Lawyers for the former Chilean dictator are presenting their case to five Law Lords - the highest adjudicating court under English law - and asking them to set aside the decision of another panel of Law Lords.

They are arguing that the earlier ruling that General Pinochet did not have diplomatic immunity must be set aside because of bias.

The appeal is based on allegations that Lord Hoffmann, who cast the deciding vote in the earlier hearing, could not have fairly judged the case because of his links with human rights group Amnesty International.

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Lord Hoffmann is a director of the charitable arm of Amnesty International and his wife, Gillian, works as an administrative assistant for the human rights campaigners.

The decision by the first panel of Law Lords means the 83-year-old general is presently facing a legal battle of up to two years to prevent his extradition to Spain.

If the extradition goes ahead, he faces genocide and torture charges relating to thousands of deaths following his seizure of power in Chile's 1973 military coup.

The BBC's Jane Peel: Five Law Lords, uninvolved with the original case, will hear the arguments

But his lawyers are hoping to avert that process by having the Law Lords' decision found invalid and reversed at a second hearing.

If the Lords allow the general's case, a further hearing will have to be convened to retest the diplomatic immunity argument.

The move to challenge the Law Lords comes the day after solicitors for General Pinochet confirmed that they would be seeking a judicial review of the UK Home Secretary Jack Straw's decision to give an "Authority to Proceed" on extradition hearings.

Jack Straw: Facing judicial review

Michael Caplan, of Kingsley Napley, acting for the general, confirmed the latest legal move but declined to outline the grounds that they would lay before the court.

But such applications are normally made on the basis that the home secretary's decision was wrong in law, or that he did not exercise proper discretion while acting in a "quasi-judicial" role.

The UK Home Office has declined to comment on the decision, other than to say that the general's lawyers were "within their rights" to seek a review.

The BBC's Jane Peel: "This has never been done before"

While the legal moves continue, General Pinochet has himself made only one court appearance at the formal start of extradition proceedings last week.