A Tory Defence Minister gave Customs the go-ahead to use the elite Special Boat Squadron and a Royal Navy ship in a raid on a ship carrying four tonnes of cannabis that will now be the subject of an inquiry, it emerged last night.

Earlier yesterday it was announced that Customs and Excise officials will be investigated over the collapse of a trial of 10 men charged in connection with the massive drugs seizure.

Paymaster-General Dawn Primarolo has appointed former Treasury solicitor Sir Gerald Hosker QC to head the inquiry into what the trial judge described as a ''catalogue of flawed proceedings, illegalities, and incompetence''.

The trial followed a raid led by the SBS on the Maltese-registered Simon de Danser 100 miles off the Portuguese coast in May 1997. It was found to be carrying cannabis with a street value of #14.5m.

But the case at Bristol Crown Court collapsed in disarray seven days ago without a jury being sworn in.

Last night, Armed Forces Minister Doug Henderson said in a Commons written reply that ''in response to a request for assistance from HM Customs and Excise, military assistance in support of this UK counter-drugs operation was authorised at ministerial level by the previous administration''.

He revealed it cost Customs and Excise #127,000 for use of HMS York and SBS personnel.

A Defence Ministry spokesman refused to name the Minister involved. ''It is not something that we would comment on,'' he said.

The trial judge accepted the vessel had been boarded in international waters without being given proper permission by the Maltese authorities, who were misled about the location of the ship.

The 10 accused included four former Royal Marines. The Crown Prosecution Service dropped efforts to extradite another man from Spain following the collapse of the case.

The chairman of the commissioners of Customs and Excise, Dame Valerie Strachan, said yesterday: ''It is important that lessons from this case should be identified and acted on. That is why I have commissioned this inquiry.''