The paper says the evidence shows that the bombing of the jumbo jet was ordered in revenge for an American air raid on Tripoli two years earlier.

But the newspaper says it was unable to publish full details after the intervention of the government's Treasury solicitor.

It says the government issued a last-minute "gagging order" against the paper, preventing it from publishing details of an intelligence operation that produced clear evidence of Gadaffi's personal involvement.

'Evidence kept secret'

All 259 people on board the Pan Am 103 plane died, as well as 11 people in the Scottish village of Lockerbie.

The trial of two men accused of planting the bomb will take place before a Scottish court sitting in Holland.

The newspaper quotes an unnamed former senior intelligence officer as saying: "We have known for a long while that Gadaffi gave the order. It is a sham for him to pretend otherwise and it is an even bigger sham for the British Government to let him off the hook."

Gadaffi: The Sunday Times alleges he ordered the bomb attack

Its report states that during the three-year joint British and American investigation into the bombing, which took place in December 1988, there was speculation that Iran and Syria were also involved.

These suspicions persisted, it says, partly because evidence was kept secret.

But it states that the security services believe Libya was solely responsible, and that Gadaffi ordered the bombing after the raid on Tripoli.

The newspaper also quotes a letter from the Treasury solicitor, warning that its information "plainly came from a member of the intelligence community", and if published could "be extremely damaging".

The letter warned that the government would seek an immediate court injunction against the newspaper unless it was assured that details of the intelligence or how it was obtained would not be printed.

The Sunday Times says its revelations come as Foreign Secretary Robin Cook is preparing to rehabilitate Gadaffi after the decision to hand over the two Lockerbie bombing suspects for trial.

'Government is very foolish'

The paper's report includes angry reaction from opposition MPs to the government's handling of the revelations.

David Wilshire, Conservative MP for Spelthorne and a member of the foreign affairs select committee, is quoted as saying: "If there is the slightest bit of truth in this, then the government is very foolish to start normalising relations with Libya.

"Some of us would argue that Gadaffi should be on trial as well."

A Foreign Office spokesman said: "We cannot comment on any intelligence matters and we never do.

"On the Lockerbie case, that is a matter for the Scottish courts and is sub judice, so there is no way we can comment on that."