Three senior judges yesterday ordered 45 pieces of key evidence to be handed over to the legal team representing the man convicted of the Lockerbie bombing in an embarrassing setback for the Crown Office.

The vital documents include a secret fax that could discredit a key prosecution witness.

The court of criminal appeal in Edinburgh ordered prosecutors to find and disclose the different evidence, which has so far been kept secret from the defence.

Last month lawyers for Abdelbaset Ali Mohmed al Megrahi, the man convicted of the 1988 bombing, began the challenge over material they believe will free their terminally ill client.

But the Crown Office and the UK Advocate General claimed that in some cases the evidence does not exist or is irrelevant.

The Libyan's defence team applied to see 48 documents, which included a fax they claim places a fundamental question mark against the original trial testimony of Tony Gauci, who sold clothes later found in the wreckage of PanAm 103 at Lockerbie.

The judges rejected three of the requests, including demands for information about the number of times police and US agencies had contact with Mr Gauci.

However, the onus will now be on the Crown to identify and share a range of other undisclosed documents, including those expected to show that Scottish police recommended to US authorities that both the main witness in the trial and his brother should be paid a reward of up to $3m, or $1.5m.

Lord Hamilton, the Lord Justice General, who was sitting with Lord Kingarth and Lord Eassie, said: "Without expressing any view on the adequacy of the steps already taken by the Crown to satisfy the claims for recovery, we consider that the appropriate course at this stage is to identify the classes of document which, if they exist, the appellant is in our judgment entitled to recover."

Megrahi's appeal is due to begin on April 27 and could last at least 12 months. Megrahi, who is suffering from advanced prostate cancer, is determined to clear his name but it is far from certain that he would survive such a long appeal case.

Libyan authorities have been encouraged to apply for a prisoner transfer to allow Megrahi to spend his remaining time with his family, but this would mean dropping the appeal, which he is not prepared to do.

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