Roderick McLean senior, 55, who was a key player in the plan to land three tonnes of cannabis worth up to �10m in Scotland, had his prison term reduced from 28 years to 21.

Gary Hunter, 36, a professional diver, also had seven years cut from the 24-year term imposed on him by Lord Dawson.

Officers found cannabis worth up to �10m

They were part of an international gang caught at sea off the Caithness coast in July 1996 which resulted in the death of customs officer Alastair Soutar.

Mr Soutar (47) from Dundee, was crushed between a customs cutter and the booby-trapped Ocean Jubilee, crewed by McLean and Hunter, which was set alight.

Lord Dawson told the pair and six co-accused when he sentenced them in 1997 at the High Court in Edinburgh that they were involved in a major league smuggling operation.

The judge told McLean he had placed flares and accelerants among the contraband cargo with the intent of destroying it if they were intercepted at sea.

Lord Dawson said: "You put this deadly plan into operation, endangering the lives of a number of officers bravely doing their duty and causing the death of one such officer."

Culpable homicide

But lawyers argued the pair should not have been sentenced on the basis that they caused Mr Soutar's death. It was also pointed out that the Crown did not charge them with the culpable homicide of the customs officer.

The Lord Justice Clerk, Lord Cullen, who heard the appeal with Lords Kirkwood and Hamilton, said they found the trial judge's reference to the cause of Mr Soutar's death "disturbing".

The senior judge added: "We have come to the conclusion that he misdirected himself in this respect."

Customs officer Alastair Soutar died in the raid

Lord Cullen said the appeal court had decided to cut two years from the sentences imposed on both McLean and Hunter for drug smuggling as they were both first offenders.

A further five years was taken off the sentences imposed on them for the additional charge of attempting to defeat the ends of justice and endangering the lives of customs officers.

Other members of the gang, which included three Dutchmen and an American, still have appeals outstanding.

Mr Soutar's sister, Eleanor Lews, said she was "sickened" by the decision.

She said: "I feel sick, just sick. Hunter was one of the main men involved. They deserved everything they got.