His father, also Duncan Lindsay (60), said his son would often go “walkabout”, but had never been gone longer than two weeks and would always make contact with someone.

He had told his mother he intended going camping to Letham, but police have been unable to confirm he went through with these plans.

The former Black Watch soldier left the army in 1982 and has a number of injuries from his time in the Forces, including the loss of his pinkie and ring fingers.

His injuries are distinctive, and he has also had a skin graft on his left hand, on which he often wears a glove.

He served mainly in Northern Ireland and continued to live in the Warrenpoint, Neury, area with his then girlfriend for a number of years after leaving the army. His father said he used to travel back to Northern Ireland, where he has a number of friends,but hadn’t done so for some time and he had “no idea” if he would have gone there.

“His mother said he bought a new tent and he has all the camping gear,” said Mr Lindsay.

He said his son often took off on camping trips.

“I would urge him to get in touch with anyone to let us know he is okay and then he can go off again on his walkabout if he likes. We need to know he is okay.

“I wasn’t worried to begin with, but as time goes on it’s becoming more worrying. The police are involved and are making inquiries.”

Police were alerted on July 11 and have since made extensive inquiries in both Letham, Angus and Letham, Fife, and have spoken to people at campsites in both areas as well as owners of shop and licensed premises — but there have been no confirmed sightings of Duncan.

Police have also made enquiries in Northern Ireland and have been in touch with his ex-girlfriend.

Detectives have investigated a possible sighting of Duncan in Forfar on Saturday, July 8.

They spoke to the witness, but CCTV failed to identify the person she saw in The Cross area of the town.

It was the day of the Farmers’ Market and detectives have urged anyone else who may have seen Duncan that day to contact them.

Detective Sergeant Colin Gaul said, “It’s over seven weeks since he went missing and that in itself is completely out of character. He keeps in regular contact with his family, if not personally, certainly by telephone.”

Duncan had an altercation with a neighbour before he went missing, but DS Gaul said they were not linking the dispute with his disappearance.

“At this time we are treating Duncan’s disappearance as a missing person,” he said.

DS Gaul said Duncan took regular medication, but it was not essential for his survival.

Duncan, who has a Grim Reaper tattoo on his right shoulder, was last seen wearing a blue tracksuit with white stripes down the arms and legs and a blue baseball cap.

Anyone who has seen Duncan or knows of his whereabouts should contact Tayside Police on 01382 223200.