Kenny MacAskill claims Jack Straw admitted commercial interests were at heart of Megrahi talks

Mr MacAskill also admitted for the first time that the Scottish Government tried to secure its own deal over Megrahi.

Read more: Megrahi family back new bid to clear his name

In a new book he says that he and former First Minister Alex Salmond demanded concessions from the UK Government in return for not making a fuss.

These included the devolution of firearms legislation and a curb on lawsuits from former prisoners forced to ‘slop-out’ using buckets in their cells.

But their attempts proved unsuccessful.

Mr MacAskill also admits he decided to release Megrahi in part to avoid reprisals if he died on Scottish soil.

And argues that Libya, Syria, Iran and Palestinian terrorists were behind the bombing, in revenge for the downing of an Iran Air flight by a US naval ship in July 1988.

All 259 people on board and 11 on the ground where killed when a Pan-Am airliner exploded over Lockerbie in 1988.

Dr Jim Swire, whose daughter Flora was one of those who died, said: "I have no doubt that they (the UK Government) were trying to what has been revealed by Kenny MacAskill, and that is to secure oil reserves in Libya for BP through the agreement of the prisoner transfer.

Read more: "I am not guilty" - Megrahi's dying words to his family

"It was all orchestrated for commercial reasons."

He added: "I am pleased to see Mr MacAskill outline his view on who was really responsible for the Lockerbie bombing, as it is clear to me it was carried out by the Iranians and Palestinian factions in response to the downing of an Iranian airbus by the USS Vincennes in 1988."

But Robert Black, the architect of the Camp Zeist trial which convicted Megrahi, said that nowhere in the extracts of the book published in the Sunday Times was there mention of the Scottish Criminal Cases Review Commission’s findings on six grounds that the conviction might have amounted to a miscarriage of Justice.

In The Lockerbie Bombing: The Search For Justice, to be published later this month, Mr MacAskill accuses the UK Government of signing a "Faustian Pact" as part of the ‘deal in the desert’ between Tony Blair and Libyan leader Colonel Muammar Gaddafi in 2007.

Mr MacAskill writes that in a later telephone call: "He [Straw] ... told me that the Libyans would not accept a PTA (Prison Transfer Arrangement) that specifically excluded Megrahi... he then went on to explain the crux of the matter as he saw it, which was British interests. A commercial deal for development of Libyan oil and other resources in the south of that country was of potentially huge financial benefit. The UK was very eager to secure the deal for BP, but it was dependent on the PTA”.

The PTA deal went ahead.

Read more: Megrahi WAS guilty of Lockerbie atrocity, says Scotland's top law officer

But as it was being agreed Megrahi was diagnosed with terminal prostate cancer and freed on compassionate grounds in 2009.

He died in Libya three years later.

Mr Straw rejected MacAskill's comments as "highly embroidered”.

Mr Salmond said that his government "played the whole thing with a straight bat from start to finish".

A spokesman for BP said the company had no comment on the UK government's actions or discussions.

An SNP spokesman said that Mr Megrahi's release was on medical grounds alone.

“Political , economic and diplomatic considerations played no part in the SNP Government's decision.

"The same cannot be said of the UK Labour Government, which cosied up to Gaddafi and his regime when Jack Straw was in charge of the Foreign Office.”

A spokesman for the Scottish Conservatives said that if Mr MacAskill thinks he's solved the crime “he should be going to the police instead of the press”.

He added: "People will be suspicious that this is a sacked justice secretary trying to recover his reputation from the premature release of the Lockerbie bomber which, even by his standards, was an absolute farce.”