Semtex finding may be tip of iceberg

Leading criminal lawyers believe evidence of contamination found in the Forensic Explosives Laboratory may have threatened the safety of many more convictions than the 12 cited by the Government.

Bindmans partner Neil O'May, who is reassessing the explosives cases he has handled, said last week's admission that laboratory equipment had been contaminated with RDX, a constituent of Semtex, was "far more damaging than seems to have been appreciated".

The Government admits "a small theoretical possibility" that cases involving RDX may have been affected by the contaminated centrifuge. Home Secretary Michael Howard said in a statement: "On present information there may be around a dozen such cases which resulted in convictions."

O'May said that in terms of evidence, the amount of RDX found in the laboratory was "huge". He argued that it indicated that the centrifuge must have been in contact with substantial amounts of Semtex.

He said this would make tests on other components of Semtex, including PETN and nitroglycerine, unreliable.

Barrister Kenneth MacDonald, who specialises in explosives cases, agreed: "There have been around 500 tests in that machine since 1989 and every single test is now suspect."

Referring to reports that the centrifuge in question was bought second hand, MacDonald said there was a danger that the verdicts in some of the most famous terrorist trials had been thrown into doubt simply to save a few hundred pounds.

Rock Tansey QC, head of 3 Gray's Inn Square, said the news of contamination "must create great anxiety in people's minds". O'May feared an enquiry, headed by forensic scientist Professor Brian Caddy, may be a damage limitation exercise.

A Home Office spokesman said the terms of reference will enable the professor to carry out a rigorous enquiry. "It is important to guard against uninformed speculation about the possible implications," he said.