No reasonable jury could have convicted the late Abdelbaset al-Megrahi of the Lockerbie bombing, appeal court judges have heard.

The bombing of Pan Am flight 103, travelling from London to New York on December 21 1988, killed 270 people in Britain’s largest terrorist atrocity.

Former Libyan intelligence officer Megrahi, who was found guilty in 2001 of mass murder and jailed for life with a minimum term of 27 years, was the only person convicted of the attack.

A third appeal against his conviction began at the High Court in Edinburgh on Tuesday.

Lockerbie Plane Crash
The Lockerbie bombing claimed 270 lives (PA)

Claire Mitchell QC, representing the Megrahi family, said the original trial court agreed the disaster was caused by the explosion of an improvised explosive device in a Toshiba cassette player.

It was in a brown Samsonite suitcase along with various items of clothing that were bought at Mary’s House in Malta.

The court heard that during the trial, shopkeeper Tony Gauci gave evidence that a man resembling Megrahi had purchased the items of clothing at his store.

She said the Crown case in the original trial was that the suitcase was loaded on to flight KM180 at Luqa airport, Malta, which flew to Frankfurt.

The bag was then transferred to a feeder flight for Pan Am 103 from London and on to that flight itself.

She said the Crown case did not establish how the suitcase, referred to as the “primary suitcase”  was loaded on to the flight from Malta.

Ms Mitchell said: “The absence of any other explanation of the method by which a primary suitcase might  have been placed on board KM180 is a major difficulty for the Crown case and one which has to be considered along with the rest of the circumstantial evidence.

“That is a critical issue because I say in this case that the way in which that major difficulty was overcome was by the court making the finding that on December 7 the appellant (Megrahi) purchased the clothing, which was found in the suitcase containing the bomb.”

Abdelbaset Ali Mohmed Al Megrahi
Megrahi, who was found guilty in 2001 of mass murder and jailed for life with a minimum term of 27 years, was the only person convicted of the attack (Cown Office/PA)

Appeal judges heard the trial court found the reliable parts of Mr Gauci’s evidence were the person who purchased the clothes was Libyan and the clothes were bought from his shop.

The High Court heard on Tuesday that Mr Gauci said Megrahi resembled the buyer but did not make an unequivocal identification.

Ms Mitchell said there were questions over whether the date of the purchase was December 7 1988, a date when the Crown could prove that Megrahi was in Malta, or a different date.

In particular, she highlighted discussions over when Christmas lights had been up, which left “the date of purchase on a shoogly peg”.

Ms Mitchell said the date hinges on whether the lights were up and if it was two weeks before Christmas as stated in Mr Gauci’s evidence – though in a police statement he had said they were not up.

Lord Carloway asked if it had since been established when the lights were put up, to which Ms Mitchell replied it had been due to a retrospective investigation but  the original trial did not know the date.

Ms Mitchell said there was “no consistency” with the witness’ evidence which was “so muddled that no evidence could be … relied upon to bear the weight of any conviction”.

She also highlighted the weather around December 7, with Mr Gauci saying it was not raining on the day of purchase but “simply dripping” – and that the man who had visited the shop bought an umbrella.

But Major Joseph Mifsud, working at Luqa Airport in Malta, gave evidence saying there was 90% no rain and the remaining 10% he said would be “some drops” in other places.

Ms Mitchell added he said a decrease in pressure meant there would be less likelihood of rain there and the ground would not be damp as Mr Gauci had also stated.

She repeatedly suggested the evidence given did not reach the necessary base level of quality to be considered.

The QC told the court: “It is submitted in this case that no reasonable jury, properly directed, could have returned the verdict that it did, namely the conviction of Mr Megrahi.”

An appeal against Megrahi’s conviction was lodged after the Scottish Criminal Cases Review Commission (SCCRC) referred the case to the High Court in March, ruling a possible miscarriage of justice may have occurred.

Judges then granted his son, Ali al-Megrahi, permission to proceed with the appeal in relation to the argument that “no reasonable jury” could have returned the verdict the court did, and on the grounds of non-disclosure of documents by the Crown.

The appeal, which is taking place virtually, began on Tuesday and is being heard before five judges including Lord President Lord Carloway.

He said the court has refused to allow the defence to recover two protectively marked documents (PMDs) held by the UK Government, which are covered by public immunity certificates.

At a hearing in August, lawyers for Megrahi’s family said it is “in the interest of justice” that the defence get to see the two PMDs.

In a written opinion on Friday, judges refused to order recovery of the documents, saying they accepted that disclosure of the PMDs would cause “real harm to the United Kingdom’s international relations” and “real harm to the national security of the UK because it would 14 damage counter-terrorism liaison and intelligence gathering between the UK and other states”.

Megrahi’s first appeal against his conviction was refused by the High Court in 2002 and was referred back five years later following an SCCRC review.

He abandoned this second appeal in 2009, shortly before his release from prison on compassionate grounds while terminally ill with cancer.

Megrahi returned to Libya and died in 2012.