This is just part of the continuing investigation into the disappearance

Detective Inspector John Ashworth

At Winchester Crown Court in 2001, 43-year-old Grimson admitted killing naval rating Nicholas Wright, 18, from Leicestershire, and barman Sion Jenkins from Newbury, Berkshire.

He tortured and bludgeoned to death the young men at his Portsmouth flat after picking them up from a nightclub on separate occasions.

Grimson was described by Mr Justice Cresswell as "a serial killer in name, if not in number".

A Hampshire police spokeswoman confirmed detectives interviewed Grimson - who is serving a life sentence - over the disappearance of Mr Parkes.

Grimson: Serving life for murder

"Grimson is one of our lines of inquiry," she said.

Police looked at 20 cases of missing sailors around the world, at the time of their inquiries into Grimson.

In April, Mr Parkes' parents, David and Margaret, went to Gibraltar and appealed for information about their missing son.

A team of four officers from Hampshire Police will be working in the colony for the next seven days.

Several areas will be searched and some excavation work will also be carried out.

Detective Inspector John Ashworth, in charge of the British side of the inquiry, said: "This is just part of the continuing investigation into the disappearance.

"We are going to Gibraltar to carry out further inquiries."