One significant reason for the appeal is that Tony Gauci, who picked al-Megrahi out in a line-up, had looked at a magazine photograph of him just four days before he made the identification.
BBC TV programme The Conspiracy Files: Lockerbie has now seen documentary evidence that Scottish police knew this was the case.
That information should have been passed to the defence, but the disclosure did not take place.
In the same programme Saif al-Islam al-Gaddafi, the son of Libyan leader Colonel Muammar Muhammad al-Gaddafi, who many believe is being groomed to succeed his father, has called the families of the 1988 Lockerbie air disaster "greedy" and "materialistic".
Miscarriage of justice?
Pan Am flight 103 from London to New York was blown up by a bomb on 21 December 1988.
All 259 passengers and crew were killed along with 11 people on the ground in Lockerbie, in Britain's worst air disaster.
Al-Megrahi is serving a life sentence in Greenock prison for the bombing
Al-Megrahi was convicted of the murders on 31 January 2001 after a lengthy investigation by the Scottish police and the FBI, and a nine-month trial at a specially convened Scottish court sitting in the Netherlands.
But there have always been doubts expressed about who was behind the bombing and what was their motivation.
In June last year the Scottish Criminal Cases Review Commission (SCCRC), which has been investigating the case, concluded that al-Megrahi could have suffered a miscarriage of justice and recommended that he should be granted a second appeal.
The specific terms on which the recommendation was made have never been fully published.
The prosecution case was that al-Megrahi took the bomb, wrapped in clothes bought from a shop in Malta, to the island's Luqa airport, where it was checked in and then transferred onto Pan Am flight 103.
A key witness against al-Megrahi was the Maltese shopkeeper Tony Gauci, who owned Mary's House, where the police say the garments were bought.
This image was seen by Tony Gauci days before he picked al-Megrahi out
He identified al-Megrahi as having been in his shop some weeks before the bombing.
The Conspiracy Files: Lockerbie reports that some of his evidence contradicted itself and that Mr Gauci had seen al-Megrahi's photograph in a magazine under a headline "Who planted the bomb?" a few days before he picked him out at an identity parade.
The SCCRC discovered this was the case, and this is one of the grounds on which they recommended that the case should be looked at again.
The BBC programme has discovered that the Scottish police knew Mr Gauci had looked at al-Megrahi's photograph just days before the line-up.
But contrary to police rules of disclosure, designed to ensure a fair trial, this crucial information was not passed on to the defence.
Mr al-Gaddafi, who carries out political and diplomatic roles on behalf of his father, was interviewed in the programme about whether Libya truly accepts guilt for the Lockerbie bombing.
I think they were very greedy and I think they were trading with the blood of their sons and daughters
Saif al-Islam al-Gaddafi
He admitted to the programme's producer Guy Smith that the Libyan government had merely accepted responsibility for the Lockerbie bombing in order to get international sanctions lifted.
"Yes, we wrote a letter to the Security Council saying we are responsible for the acts of our employees... but it doesn't mean that we did it in fact.
"I admit that we played with words - we had to.
"What can you do? Without writing that letter we would not be able to get rid of sanctions."
When Guy Smith put it to him that this was a cynical way to conduct foreign policy, he launched into an attack on the families of the Lockerbie victims.
"You have to ask the families of the victims. The negotiation with them, it was very terrible and very materialistic and was very greedy. They were asking for more money and more money and more money".
He said: "I think they were very greedy and I think they were trading with the blood of their sons and daughters."
Truth 'not out'
After the Libyan government agreed to pay $10m (£5.3m) per victim in compensation, sanctions against Col Gaddafi's regime were lifted and diplomatic ties renewed.
No one is trading a life for money. Every one of the clients would give back every penny received from Libya and from Pan Am had their family members not been killed
Dr Jim Swire, whose daughter Flora died on Pan Am 103 said: "From within Western culture Saif al-Gaddafi's comments will be found deeply offensive by some relatives, but I can see this as the Arab way of doing things.
"The Libyans have achieved what they want - and Western commerce has got what it wants too. In this, many of us feel like pawns."
Former Prime Minister Tony Blair has visited Col Gaddafi, and the man who used to support terrorism against the West has now been welcomed as an ally in the so called "war on terror".
But ever since the Lockerbie bombing, conspiracy theories have circulated about who was behind the terrorist attack and what was their motivation.
Martin Cadman, whose son Bill died in the disaster, told the programme: "The truth has not come out. I think the investigation found what it was told to find".
Al-Megrahi's appeal is expected to be heard early next year.
The Conspiracy Files: Lockerbie was broadcast on Sunday, 31 August, 2008 at 2100 BST on BBC Two.
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