And recent letters to the secretary of the group, Pamela Dix - whose brother died at Lockerbie - from Baroness Symons, minister of state at the Foreign Office, and from the Crown Office in Edinburgh, have argued that any further questions to the Libyans about Lockerbie would not be helpful. In short, ministers took the credit of the families' support without asking a single question about Lockerbie to justify that support. In a sense of deep outrage, the families are asking the prime minister for a meeting to discuss Lockerbie as a matter of urgency.

More people died at Lockerbie than in Madrid, and you would have thought that the government, if only as proof of its horror at terrorism, would be keen to question its new friends in Tripoli about the bombing. Not so, apparently. So the only hard information the families have is that Abdul Basset al-Megrahi, a Libyan official, apparently working in intelligence, was convicted in January 2001 of bombing the airliner. How he accomplished this feat is still a mystery. The details of the crime did not emerge at the trial, which was held by Scottish judges sitting without a jury in Holland. It lasted 18 months and cost an estimated £50m.

Megrahi's co-accused was acquitted, so the prosecution's suggestion that the two men conspired to bomb the plane cannot be right. Indeed, the crucial evidence that the bomb was put on a feeder flight at Malta and was transferred twice, at Frankfurt and at Heathrow, was so thin it was derisory.

No one knows whether anyone else took part in this sophisticated crime of terror. One man has been convicted. The Libyan government has forked out many millions in compensation. And that, apparently, is the end of the matter. Many of the bereaved relatives, including Dix, are increasingly disturbed at the behaviour of ministers who talk business and politics to the Gadafy regime, but are not remotely interested in pressing anyone in it to tell the whole story about Lockerbie.

There is, in my opinion (not necessarily shared by the families), an explanation for all this, an explanation so shocking that no one in high places can contemplate it. It is that the Lockerbie bombing was carried out not by Libyans at all but by terrorists based in Syria and hired by Iran to avenge the shooting down in the summer of 1988 of an Iranian civil airliner by a US warship. This was the line followed by both British and US police and intelligence investigators after Lockerbie. Through favoured newspapers like the Sunday Times, the investigators named the suspects - some of whom had been found with home-made bombs similar to the one used at Lockerbie.

This line of inquiry persisted until April 1989, when a phone call from President Bush senior to Prime Minister Margaret Thatcher warned her not to proceed with it. A year later, British and US armed forces prepared for an attack on Saddam Hussein's occupying forces in Kuwait. Their coalition desperately needed troops from an Arab country. These were supplied by Syria, which promptly dropped out of the frame of Lockerbie suspects. Libya, not Syria or Iran, mysteriously became the suspect country, and in 1991 the US drew up an indictment against two Libyan suspects. The indictment was based on the "evidence" of a Libyan "defector", handsomely paid by the CIA. His story was such a fantastic farrago of lies and fantasies that it was thrown out by the Scottish judges.

In Britain, meanwhile, Thatcher, John Major and Blair obstinately turned down the bereaved families' requests for a full public inquiry into the worst mass murder in British history.

It follows from this explanation that Megrahi is innocent of the Lockerbie bombing and his conviction is the last in the long line of British judges' miscarriages of criminal justice. This explanation is also a terrible indictment of the cynicism, hypocrisy and deceit of the British and US governments and their intelligence services. Which is probably why it has been so consistently and haughtily ignored.

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