The former Lord Advocate Lord Fraser of Carmyllie has been challenged by Dr Jim Swire to explain his position after he told an Al Jazeera documentary film crew that he accepted a key witness in the Pan Am 103 trial was bribed by Scottish Police.

Fraser, who was Lord Advocate at the time proceedings were raised against Abdelbaset Al Megrahi and acquitted co-accused Lhamin Khalifa Fhimah, acknowledged that Maltese shopkeeper Tony Gauci appeared to have been offered financial inducements for his testimony, which ultimately placed Megrahi in Malta, purchasing clothes linked to an explosive device.

Dr Swire said he had watched the documentary, which disclosed the revelations contained in police diaries, in "astonishment", and said that it added to "defects evident in the trial itself, which indicate a dire need for reappraisal of the trial verdict."

"The Al-Jazeera programme used material from the diary of Detective Chief Inspector Harry Bell, who had performed a key role in the Scottish police inquiries in Malta. The documentary also highlighted the astonishing provision of 'all expenses paid' holidays in Scotland for the shopkeeper, before he gave his evidence," Swire said.

"During this documentary Lord Peter Fraser, who was Lord Advocate at the relevant times, explained that he was unaware of this offer of money to this key witness, at the time of the trial, but now that it seemed to have been shown to have been the case, he did not believe that the bribe, for such it surely was, had affected Gauchi's evidence given under oath in court.

"It would appear to a layman that a bribed witness's evidence should be of little value in a criminal court where 'reasonable doubt' has to be excluded.

"Perhaps initially Lord Fraser would care to explain the position he took 'on camera'," Swire concluded.

Lord Fraser has not made any comment following the broadcast.

The Parliament's petitions committee will hear the fourth presentation from the Justice for Megrahi committee of their application for a full inquiry into the debacle on 28 June.

Swire's letter can be read in full, here.