CRUCIAL new claims that could free the Libyan convicted of the Lockerbie bombing have emerged via a retired Scottish police officer of high rank who has told lawyers that vital evidence was fabricated.

The revelation could represent the most dramatic breakthrough for the legal team acting for Abdelbaset Ali Mohmed Al-Megrahi since his conviction for mass murder in 2001.

The retired officer was a member of the Association of Chief Police Officers Scotland (ACPOS), and therefore achieved the rank of assistant chief constable at least.

He has supported the evidence provided to Megrahi's lawyers by a former CIA agent that senior figures in United States intelligence wrote the script to incriminate Libya for the bombing.

The Scottish officer's validation of the claim gives it a credibility it would not otherwise have had, given the senior rank he held.

Sources close to Megrahi's legal team have said the retired officer approached them after Megrahi's appeal, before a bench of five Scottish judges, was dismissed in 2002.

One source said: "He said he believed he had crucial information. A meeting was set up and he gave a statement that supported the long-standing rumours that the key piece of evidence, a fragment of circuit board from a timing device that implicated Libya, had been planted by US agents."

Asked why he had not come forward before, he admitted he had been wary of breaking ranks, afraid of being vilified. He also said that at the time he became aware of the matter, no-one really believed there would ever be a trial.

Dr Jim Swire, who has publicly expressed his belief in Megrahi's innocence, said it was right that all relevant information should be put to the Scottish Criminal Cases Review Commission. Dr Swire, whose daughter Flora was killed in the bombing, said: "It is in all our interests that areas of doubt are thoroughly examined."