Officers concentrated their search on the Ogden Water country park, Halifax, after receiving an unconfirmed sighting of the 48-year-old near the reservoir on the day he disappeared from his home in Queensbury.

Detective Inspector Ian Bryar revealed that a member of the public had reported seeing a man matching Mr Rowling's description at about 11.30am on Saturday February 27.

VIDEO: DI Ian Bryar of Bradford South CID makes an appeal for information about Mr Rowling's disappearance

"David left home that day at 9.30am and at 11.30am we believe a member of the public saw him," he said.

"He had seen David's photo in the media and thought it was the same man he'd seen walking around the reservoir. The description does tally with what he was wearing when he left home."

Mr Rowling, described as an outdoor man, often visited the reservoir for walks and runs but was not wearing outdoor clothing when he left home.

He also had not taken any money or credit cards with him. Det Insp Bryar said Mr Rowling, of Alma Street, Queensbury, who is an IT consultant, was a very private man, with limited friends, and had been leading a normal family life with his wife and young son but had been feeling low.

The underwater search unit, using a dinghy and sonar, was scouring the reservoir while officers on foot searched surrounding woodland.

Anyone with information should ring 0845 6060606.

VIDEO: DI Ian Bryar of Bradford South CID makes an appeal for information about Mr Rowling's disappearance