The Lord Advocate Elish Angioini has refused to engage with the semtex challenge backed by UN Special Observer Hans Kochler and Professor Robert Black QC, set by the Lockerbie Justice Group.

The group have tasked Angiolini to demonstrate that a fragment of circuit board can survive a semtex blast, as claimed by the Crown in the Lockerbie trial. The group say that this is not physically possible.

Despite repeated requests for a response, Angiolini has not acknowledged the group’s challenge, and refused to engage with the gauntlet that has been thrown down.

Angiolini has also refused to be interviewed by The Firm about the challenge.

The challenge itself coincides with the screening of dutch documentary "Lockerbie Revisited" at Holyrood tomorrow night, which focuses on the crucial piece of circuit board fragment alleged to have been found during the Lockerbie investigation. The film casts serious doubts over the credibility of this evidence. It has been nominated for best documentary at the forthcoming Netherlands International Film Festival in Utrecht.

The challenge to the evidence has been emboldened by confirmation from semtex manufacturer Miroslav Štancl of Explosia a.s, who says the temperature at the point of explosion of “plastic explosives Semtex” is between 3,800 and 3,870 ° C , depending upon the type and composition.

Aitken Brotherston, who tested circuit boards as an engineer at Ferranti says that such boards will combust at temperatures equivalent to that produced by a Swan Vesta match, and “nothing would survive” within a semtex blast bright spot.

“The proposal that fragments of the board, of sufficient size to permit identification, packed with the bomb had survived a temperature environment of more than 3000 degree C in the explosion is to me just not credible,” he says.

In 2007, MEBO engineer Ulrich Lumpert submitted an affidavit stating that the circuit board fragment produced in court at Zeist was part of a non-operational demonstration circuit board that he himself had removed from the premises of MEBO and had handed over to an investigator on 22 June 1989, six months after the destruction of Pan Am 103.

“If this is true, then it totally demolishes the prosecution version of how the aircraft was destroyed, as well, of course, as demonstrating deliberate fabrication of evidence laid before the court,” Professor Black said at the time.

Lumpert’s statement is consistent with reports published in 2005 by the Scotland on Sunday newspaper in which a former Scottish police officer said “that the CIA planted the tiny fragment of circuit board crucial in convicting a Libyan.”

Earlier this year a test conducted by Dr Ludwig De Braeckeleer and researchers at the Centre of Explosives Technology Research in Socorro, New Mexico estimated that up to thirty pounds of explosive was needed to penetrate a Boeing 747, if the explosion had occurred in the hold as the Crown claimed. They concluded that the Crown’s case, which maintained only one pound of semtex destroyed Pan Am 103 was “scientifically implausible“.