A MAJOR military police investigation has taken place after a member of the Irish Naval Service was arrested for supplying information on patrol vessel movements to drug traffickers.

The man is suspected of having given precise details of the whereabouts of drug interdiction boats around the Irish coast.

Specific data on the patrol vessels meant smugglers could move large shipments of drugs, along with small amounts of weaponry, onshore safely.

The major security leak, described as "incredibly serious", was uncovered as part of standard internal checks in place to avoid the disclosure of confidential information.

Military sources said unauthorised information had been passed to unauthorised people and that the investigation was "not being treated lightly".

The member of the Naval Service at the centre of the inquiry was immediately removed from his position, where he had access to detailed drug surveillance information.

A major military police investigation then got under way, involving the help of military intelligence. Sources told the Sunday Tribune it was suspected the man had been paid for the information.

A statement from commandant Gavin Young of the Defence Forces said: "Resulting from regularly conducted security checks Naval Command became aware some months ago of information being allegedly disclosed without authority by a member of the Naval Service to civilian persons. Following a military police investigation a file has been sent to the director of military prosecutions for decision in accordance with the Defence Act 1954-2007." Young said the inquiry was being taken "very seriously".

Patrolling Ireland's massive coastline is difficult at the best of times and customs officers have the use of just two patrol vessels.

Their activities are bolstered by constant surveillance activity from the seven Irish Naval patrol vessels, which also have other core military responsibilities.

A CASA aircraft from the Air Corps is also used for surveillance operations and it carries electronic experts and photographers.

However, monitoring the entire coastline with just a handful of boats has been described as akin to "catching fleas in a butterfly net".

One garda source said: "It is a huge area of sea with hundreds and hundreds of miles of coastline. It would be difficult enough to secure at any time.

"The idea that somebody may have been passing unauthorised information like this would have effectively made it impossible."

A military source said leaks from a massive organisation such as the Defence Forces were always a concern and the key was ensuring security checks uncovered them quickly.

The scale of drug trafficking along the Irish coast cannot be underestimated and in one short period in 2007, €130m worth of drugs literally washed ashore in four separate incidents.