Nearly two decades after Pan Am flight 103 exploded over Scotland on 21 December, 1988, allegations of international political intrigue and shoddy investigative work are being levelled at the British government, the FBI and the Scottish police as one of the crucial witnesses, Swiss engineer Ulrich Lumpert, has apparently confessed that he lied about the origins of a crucial 'timer' - evidence that helped tie the man convicted of the bombing to the crime.

The disaster killed 270 people when the London to New York Boeing 747 exploded in mid-air. Britain and the US blamed Libya, saying that its leader, Colonel Muammar Gadaffi, wanted revenge for the US bombing of Tripoli in 1986. At a trial in the Netherlands in 2001, former Libyan agent Abdulbaset al-Megrahi was jailed for life.

He is currently serving his sentence in Greenock prison, but later this month the Scottish Court of Appeal is expected to hear Megrahi's case, after the Scottish Criminal Cases Review Commission ruled in June that there was enough evidence to suggest a miscarriage of justice. Lumpert's confession, which was given to police in his home city of Zurich last week, will strengthen Megrahi's appeal.

The Zurich-based Swiss businessman Edwin Bollier, who has spent nearly two decades trying to clear his company's name, is as eager for the appeal as is Megrahi. Bollier's now bankrupt company, Mebo, manufactured the timer switch that prosecutors used to implicate Libya after they said that fragments of it had been found on a Scottish hillside.

Bollier, now 70, admits having done business with Libya. 'Two years before Lockerbie, we sold 20 MST-13 timers to the Libyan military. FBI agents and the Scottish investigators said one of those timers had been used to detonate the bomb. We were shown a fuzzy photograph and I confirmed the fragments looked as though they came from one of our timers.'

However, Bollier was uneasy with the photograph he had been shown and asked to see the fragments. He was finally given permission in 1998 and travelled to Dumfries to see the evidence.

'I was shown fragments of a brown circuit board which matched our prototype. But when the MST-13 went into production, the timers contained green boards. I knew that the timers sold to Libya had green boards. I told the investigators this.'

Back in Switzerland, Bollier's company was in effect bankrupt, having faced a lawsuit from Pan Am and having lost major clients, such as the German federal police to which Mebo supplied communications equipment.

In 2001, Bollier spent five days in the witness box at the Lockerbie trial at Camp Zeist in the Netherlands. 'I was a defence witness, but the trial was so skewed to prove Libyan involvement that the details of what I had to say was ignored. A photograph of the fragments was produced in court and I asked to see the pieces again. When they were brought to me, they were practically carbonised. They had been tampered with since I had seen them in Dumfries.'