Professor Robert Black QC and UN appointed international observer Hans Kochler have backed a campaign initiated by the Lockerbie Justice Group which challenges the Lord Advocate to openly demonstrate that Pan Am 103 could have been brought down by a semtex bomb, under controlled laboratory conditions.

The group state that fabric and circuit board fragments cannot survive a semtex explosion, and accordingly the entire Crown case against Abdelbaset Ali Mohmed Al Megrahi falls. In 2007 Ulrich Lumpert of timer company MEBO released an affidavit stating he had manufactured the circuit board “evidence” relied upon by the Crown at the Zeist trial. Earlier this year a report by Dr Ludwig de Braeckeleer concluded that the Crown’s case was “scientifically implausible”.

“The Crown theory utterly depended upon Judges believing that this white-hot sphere with a temperature of 6,800F, travelling in all available directions at 20,000mph did not scorch, never mind totally annihilate, a printed circuit board and a fabric label, which it was able to wholly detach from the shirt. Our group finds this utterly incredible,” the group said.

“We, as members of the concerned Scottish public, invite the Crown to openly demonstrate their theory under controlled laboratory conditions. Either the circuit board survives with its legible ID and soft solder, or it is annihilated in a white-hot gas. In the event of PCB annihilation, we demand a proper and independent committee of inquiry into ‘What brought this plane down?’ Will you please publicly demonstrate your theory, Madam Lord Advocate?”

The challenge has been backed by Dr Hans Kochler, who observed the trial and called for a full public inquiry afterwards.

“It is highly important to address this question to the Scottish prosecutor’s office and I shall add my name to such an initiative,” he said.

“It is equally important that an explosives expert with impeccable academic credentials, ideally a University professor from a European country, endorses this initiative or confirms the basic physical facts in writing. Under this condition I can join the initiative.”

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 destroy a Boeing 747, if the explosion had occurred in the hold as the Crown claimed

“As the explosion of one pound of Semtex H inside the luggage container does not generate a blast wave sufficiently powerful to fracture the skin of the fuselage, we have little choice but to conclude that the verdict appears scientifically very implausible,” they said.

The group’s initiative is bolstered by the new testimony of former Ferranti electrical engineer Aitken Brotherston, experienced in testing circuitry for use in military applications.

“Although no doubt there have been some advances in the construction of circuit boards the predominance of boards in current use are the same as those I tested. In most cases the boards would happily catch light with a flame source similar to that of a Swan Vesta and the others merely required a butane blowtorch with temperatures being at most in 100s of degrees C,” he says.

“While we did not test them to the 3000 plus degrees C temperatures of a Semtex explosion bright spot, even as an apprentice electronics engineer with Ferranti, my experience at much lower temperatures would persuade me that nothing of the circuit boards would survive that environment.

“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.

“What it does demonstrate is the extent to which anyone promulgating that theory believes us out here in the real world to be completely stupid.”