A British millionaire is facing jail after he was convicted on Tuesday of selling fake bomb detectors to Iraq and other countries.

James McCormick, 56, was found guilty of three counts of fraud at London's Old Bailey court for selling completely ineffective devices based on an American novelty golf ball finder.

McCormick made an estimated 50 million pounds ($76 million, 59 million euros) from sales of his three models to customers that included Iraq, Belgium and the United Nations for use in Lebanon.

"The devices did not work and he knew they did not work," prosecutor Richard Whittam told jurors.

"And despite the fact they did not work, people bought them for a handsome but unwarranted profit."

McCormick was bailed until his sentencing on May 2.

He shook his head as the verdicts were delivered.

The businessman, who is from Langport in Somerset, southwest England, is believed to have made around 37 million pounds from sales to Iraq alone, while other customers included Georgia and Niger.

McCormick told the court he had also sold the detectors to the Egyptian army, Kenyan police, Hong Kong's prison service and Thai border control.

The detectors were marketed to governments around the world through glossy brochures and the Internet.

Advertising material showed the devices being used to find explosives, drugs, ivory and people.

Whittam said McCormick had made "fantastic" claims about the detectors, including that they could track objects a kilometre (0.6 miles) underground.

One of the models was sold for as much as $40,000 per unit, Whittam said.

The prosecutor told the jury that McCormick had based his designs on 300 "Golfinder" novelty machines that he bought from the United States between 2005 and 2006.

Colour-coded "sensor cards" -- orange for explosives, blue for drugs and red for humans -- were slotted into the machines to make them "work".

McCormick told the court that one of his detectors had been used to check a hotel in Romania before a US president visited in the 1990s.

"I never had any negative results from customers," the businessman said.