A huge search was launched for the pensioner after the man's boat, The Midnight Oil, was found floating unmanned and drifting 23 miles off Trevose Head, Cornwall.

A Belgian fishing boat discovered the empty vessel at 11.15am yesterday, but there was no sign of the owner.

Two lifeboats, an RAF search and rescue helicopter and a naval vessel spent yesterday scouring the area in a search effort that was co-ordinated by the Falmouth coastguard.

A coastguard rescue helicopter searched for three miles in every direction from the point where the boat was found.

It also traced the possible passage the vessel would have taken from Milford Haven in South Wales – the last known location of the boat on June 28 before it was discovered yesterday.

But the search has now been called off and police are investigating the circumstances surrounding the man's disappearance. He has not yet been named by police.

The Midnight Oil, with the 81-year-old and his son aboard, had been rescued earlier this month by Angle Lifeboat after suffering engine failure 35 miles off St Govans. She was towed into Milford Haven by the fishing vessel Oceanis and the Angle lifeboat.

The pair had been sailing from Scotland to Gosport, and the son is believed to have left the boat at Milford Haven, leaving his father to finish the journey alone.

Police from Scotland, Cornwall and Milford Haven are investigating the incident.

A police spokesman said St Ives police would be making further enquiries and were looking into whether there were suspicious circumstances surrounding the disappearance.

A Falmouth Coastguard spokesman said: 'There was no trace of the man in the water and the search was scaled down midway through the afternoon.

'We know that the boat had previously been towed into Milford Haven when it developed some faults.

'But these were apparently repaired and he was making his way to Falmouth. His son had joined him during part of the journey.

'When the boat was found drifting everything seemed in order, the engine started with no problems and the man's possessions were found inside the cabin.'

The boat has been towed into the port of St Ives.