Darwin, 57, was set on cutting a deal after seeing the £45,000, 60ft catamaran.

A £1,000 deposit was transferred from a bank account in 2005 – three years after John had vanished.

Darwin even gave the family home in Seaton Carew as a contact address to boat dealer Robert Hopkin (pictured) using the name John Jones.

Mr Hopkin, 37, said he was astonished when police called him after a paper trail led them to his office.

He said: "I never guessed he could be hiding such a secret. He did act suspiciously but he called himself Jones and had a passport to prove it."

Darwin had flown out to meet him in Gibraltar from Newcastle. The boat deal fell through after Darwin argued about the interior fittings.

Ex-pat salesman Mr Hopkin said at the time: "It's unbelievable to think I could have sold that man the boat he could have disappeared around the world on.

"I got the feeling he was keen to see as much of the world as possible and she's the kind of vessel you could go off radar in for months."

The deal fell through when the family selling the boat wanted to remove some personal items. Darwin was having none of it.

"He went mad, and before I knew it the deal was off," said Mr Hopkin. "He fired off a furious email and that was that.

"That strop could have changed the course of his life. If he'd bought that boat he'd have been off and away."