Simon Parkes was last seen in Gibraltar in December 1986

Simon Parkes from Kingswood, South Gloucestershire, was a radio operator on HMS Illustrious when he vanished in the colony in December 1986.

Then aged just 18, the naval rating left his passport, belongings and Christmas presents on board the ship when he went to visit a number of bars. He never returned.

Police re-opened the Simon Parkes case in 2001 after his shipmate, petty officer Allan Grimson, was convicted of two murders.

Since then Hampshire Police and the Royal Gibraltar Police have carried out a number of searches on the peninsula.

Petty Officer Allan Grimson was convicted of two murders in 2001

And on Monday three detectives and a naval officer will again travel to the colony to search for clues in the hunt for Mr Parkes.

"We have carried out further research work and have made an assessment of the material that was gathered during our visit to Gibraltar in January," said Detective Inspector John Ashworth.

"We have decided that there is now a need to carry out further searches in a specific area of the country."

Search dogs

He said the area to be searched during the week-long trip would not be identified.

During the force's last visit to Gibraltar, dogs from the Netherlands National Police Agency Human Remains Detection Team were used to search the South Barracks and South Pavilion Road.

Det Insp Ashworth renewed his appeal for information about Mr Parkes' whereabouts to contact him.

"The Parkes family are desperate to know what has happened to their son," he said.

"They have lived with this situation for 16 years. Someone must know what happened to Simon and we would urge them to contact police with that information."