Prosecutors are trying to keep secret 48 pieces of evidence relating to the Lockerbie trial, including a secret fax that could discredit a key Crown witness.

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

But the Crown Office and the UK Advocate General are fighting against disclosure, claiming that in some cases the evidence does not exist.

The Herald can today reveal that the first item on the list is a fax which, the Libyan's defence team claims, 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.

Judges at Camp Zeist were told that the first "photoshow" with Mr Gauci took place on September 14, 1989, while the fax at the centre of yesterday's proceedings is allegedly dated six days earlier.

Megrahi's team believes that confusion and disparity further compromises the integrity of a man described as an "important witness" at the trial.

His QC, Maggie Scott, revealed that the appeal, due to start on April 27, will be based on fresh evidence, the Lord Advocate's failure to disclose and irregularities in how evidence was obtained.

She said: "The predominant theme is Toni Gauci. He is the centrepiece in a sense."

Another previously unseen fax from the Joint Intelligence Group (JIG) or committee, which was set up after Lockerbie to investigate the case and included representatives from Scottish forces and the security services, refers to a meeting between Mr Gauci and FBI agents when Scottish police were not present. However, no record or statement has been shared with the defence.

Another JIG fax referred to yesterday indicates that there are other missing statements in relation to Mr Gauci, saying he saw the key clothes purchaser the day afterwards, and identified him as someone other than Megrahi.

That document refers to concerns among the Scottish police at the time that "the witness was trying to please them".

The defence also claims that the Crown pre-trial precognition of Mr Gauci was missing and was only recently discovered by the Scottish Criminal Cases Review Commission. The defence is also seeking "undisclosed information about discussion of reward money".

This is thought to relate to undisclosed discussions that Mr Gauci and his brother, Paul, could be influenced by the rumour of financial remuneration.

Ms Scott warned that there was a "reasonable" or "real" possibility that the Crown's failure to hand over the material could constitute a breach of article 6 of the European Convention on Human Rights, relating to a person's right to a fair trial.

She explained that, in its written responses to the defence, the Crown had argued that in some cases the calls for information were too wide, in others that the information does not exist and/or that it is not relevant. The hearing continues until at least tomorrow.

The Crown has not yet responded, but is understood to be refusing to disclose details of the September 8 photoshow, along with 47 other areas of information.

Megrahi's appeal itself 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.

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