The cocaine was found in bales of rubber

James Mair, 38, William Grant, 38, David Frew, 55, and Sean McAdam, 36, were convicted last month of trying to smuggle the drugs, worth �25m, through the Suffolk port of Felixstowe.

At the High Court in Edinburgh on Friday, Lord Carloway told them they had been convicted of "an elaborate scheme which was only foiled by the vigilance of Customs and Excise officers".

He added: "The courts must do what they can to discourage the illegal trade in class A drugs and it has been repeatedly said that severe sentences will be imposed on those caught in this operation.

"The reason is because the importation of class A drugs into this country leads to so many other crimes, both of dishonesty and violence."

Mair, of Cumnock, Ayrshire, and Grant, from Bothwell, Lanarkshire, were both sentenced to 18 years.

Frew, from Kilmarnock, Ayrshire, was sentenced to 12 years' imprisonment, while McAdam, who is also from Kilmarnock, was jailed for 10 years.

The men remained impassive in the dock, although some members of their families in the public benches gasped as the judge passed sentence.

SENTENCES James Mair - 18 years William Grant - 18 years David Frew - 12 years Sean McAdam - 10 years

During their 18-day trial at the High Court in Glasgow, it emerged that the cocaine, which weighed 1,100lb, had been hidden in bales of raw rubber exported from Panama.

Mair and Grant were convicted of smuggling the cocaine and being concerned in its supply in Scotland.

Frew and McAdam played a lesser role, but were convicted of smuggling and being involved in the supply of cocaine.

A fifth man, McAdam's brother William, 40, of Abbots View, Kilwinning, was acquitted with a unanimous not guilty verdict.

The court heard that Mair, who owned a small goods delivery business, allowed his rented premises in the Buchanan Business Park at Stepps, Glasgow, to be used as a front for the operation.

Documents showed that the rubber was ordered in his company's name and that he had used fake faxes to legitimise the cargo by making it look as if it was destined for a rubber company in Dumfries.

Mair and Grant, who ran a similar small delivery business, organised the loading and unloading of the rubber bales and their transportation to an industrial estate storage unit in Kilwinning.

Rubber bales

A sixth Scot, from Kilmarnock, who cannot be named for legal reasons, was said to have helped to mastermind the operation. A Scots warrant and an Interpol "red notice" have been issued for his arrest.

Customs officers became suspicious when they learnt that a cargo of raw rubber was bound for the Suffolk port of Felixstowe from Panama in the container ship Magleby Maersk.

When the bales were unloaded last September, officers unbolted the containers and used X-ray machines to discover secret compartments in 125 of them.

They then replaced the cocaine with sand and allowed the containers to be sent to Scotland under surveillance.

After a week in the Stepps unit, half the consignment was loaded on to a white van and driven by Frew to the Kilwinning storage unit.