The timer which detonated the Lockerbie bomb was critical to the Crown case against Abdelbaset Ali Mohmed al Megrahi.

Much of the case was largely circumstantial but the prosecution argued that a small fragment of green circuit board found embedded within the charred remains of a shirt collar matched a distinctive model of electronic timer, known as the MST13.

The timers were designed and built by a small Swiss company called Mebo and, according to the prosecution, supplied solely to Libya.

The fragment was found by forensic scientist Dr Thomas Hayes of the Royal Armaments Research and Development Establishment, on May 12, 1989.

The trial court accepted the evidence given by one of the partners in that firm, Edwin Bollier, that in 1985 and 1986 he had supplied 20 sample MST13 timers to Libya. However, at least two of the same timers were also supplied to the East German Stasi secret police.

Doubt was cast at the original trial about the veracity of the forensic examination of the fragment, including the fact that the description on the label had been changed from "cloth" to "debris" and the alteration had not been signed.

The court transcript states: "On the evidence which we heard, we are satisfied that the explosive device which destroyed PA103 was triggered by an MST13 timer alone."

The court dismissed the possibility that the Popular Front for the Liberation of Palestine-General Command, the original suspects in the case, had obtained such timers via their German cell.

Last month, The Herald revealed that the makers of the timer plan to travel to Scotland following the revelation that one of their employees planted vital evidence.

Ulrich Lumpert, formerly an electronics engineer with Mebo in Zurich, signed an affidavit admitting that he committed perjury before the Scottish Court in the Netherlands.

In his affidavit, he states that he stole a handmade sample of an "MST13 Timer PC board" from Mebo in Zurich and handed it over to an "official person investigating the Lockerbie case" on June 2, 1989.