The case against the only man convicted of the Lockerbie bombing could collapse, the politician who controversially freed him has warned.

Former Scottish justice secretary Kenny MacAskill spoke out after the Scottish Criminal Cases Review Commission (SCCRC) announced a full review of the case is to be carried out to decide if a fresh appeal against Abdelbaset al-Megrahi's conviction can be made.

Mr MacAskill said the evidence of Maltese shop-keeper Tony Gauci, which was critical in the case against Megrahi, was only of the "issues to investigate" after it emerged the witness "received substantial sums of money for his testimony".

READ MORE: Lockerbie bomber case to be reviewed

Writing in the Scotsman newspaper, Mr MacAskill said it was "hard to see" how this evidence could be accepted "given that it's unprecedented in Scots Law and that the court in the same trial castigated the evidence of a paid CIA informer".

He added: "If it falls, then the case against Megrahi almost certainly collapses."

Mr MacAskill said: "That doesn't mean that those who prosecuted him or convicted him were at fault. In my view, all involved sought to act appropriately in what was an extremely difficult case."

Megrahi, who died of cancer at home in Libya in 2012, had abandoned a previous appeal against his conviction in the run-up to his release from prison on compassionate grounds in Scotland in 2009.

He remains the only person ever convicted for the bombing of Pan-Am flight 103 in December 1998, which killed 270 people.

The Libyan was jailed for 27 years after being found guilty following a trial held at a specially convened court in the Netherlands under Scots law in 2001.

Mr MacAskill, whose decision to release Megrahi sparked anger amongst many of the victims' relatives, said he believed while the Libyan "wasn't the bomber" he did have a "peripheral role" in the atrocity.

"It's one thing to argue the conviction was unsafe, but quite another to say that he had no involvement," the former justice secretary said.

He also said if the case does return to court for a second appeal, it would be "interesting" to see if new evidence emerges.

READ MORE: Lockerbie bomber case to be reviewed

Mr MacAskill said: "Since the fall of Gaddafi, the CIA and MI6 have obtained documentation from Libya, as well as locating key witnesses and removing them from the failed state. They're now available, but will they be produced?

"In particular will Moussa Koussa, Libya's former foreign minister, appear? He defected with the help of MI6 and now lives in Qatar."