Adrian Shine, leader of the Loch Ness Project, travels on the boat towing Munin, an intelligent marine robot, at Loch Ness in Scotland on April 13, 2016. Picture: REUTERS/Russell Cheyne

Edinburgh - A high-tech marine drone scouring the depths of Scotland's Loch Ness for one of nature's most elusive beasts has found a “monster” - but not the one it was looking for.

Rather than the fabled Loch Ness Monster itself, the probe has discovered a 30-foot (9 metre) replica used in the 1970 film “The Private Life of Sherlock Holmes,” which sank nearly 50 years ago after its buoyant humps were removed.

Undeterred, the enthusiastic monster-hunters steering the drone are continuing their two-week search for any evidence that might prove the existence of “Nessie”.

The survey by Norwegian company Kongsberg Maritime has been the most detailed to date of the Loch's icy depths.

The Munin drone is capable of mapping vast areas down to 1 500 ft (457m) and is often used to locate downed aircraft.

“The vehicle allows sonars to scan just a few metres from the loch floor, giving resolution several orders of magnitude greater than anything before,” said Kongsberg Maritime engineer Craig Wallace.

Along with the movie replica, it has also found a 27-ft (8.2m) shipwreck as it maps the Loch floor.

Far from being disappointed by the findings, Steve Feltham who has been hunting Nessie for 25 years, says the maps will help him in his quest.

“I think the findings are fantastic,” he said. “We now have a more detailed map of the rock bottom than ever before, which will show us the location of every lump and bump.

“We can send back cameras to look at anything of interest which could turn out to be the carcass of the animal,” he added. “It's shown there's a hell of a lot more to investigate.”

The first written record of a monster relates to the Irish monk St Columba, who is said to have banished a “water beast” to the depths of the River Ness in the 6th century.

The most famous picture of Nessie, known as the “surgeon's photo”, was taken in 1934 and showed a head on a long neck emerging from the water.

It was revealed 60 years later to have been a hoax that used a sea monster model attached to a toy submarine.

Countless unsuccessful attempts to track down the monster have been made in the years since, notably in 2003 when the BBC funded an extensive scientific search that used 600 sonar beams and satellite tracking to sweep the full length of the loch.

It concluded there was probably nothing there.