A salesman accused of marketing useless bomb detectors told a court he believed the machines were “amazing”.

Simon Sherrard, 50, of Hill Rise, Hampstead Garden Suburb, sold devices made by a couple in their semi-detached home to security services around the world.

They sold for up to £13,200 a piece but were in fact useless and the scientific principle they were said to work on was “total nonsense,” the Old Bailey has heard.

But Sherrard yesterday told the court he was convinced the bomb detectors worked after seeing several demonstrations and testing the Alpha 6 machine for himself.

He said Sam Tree, 66, who manufactured the device, showed him how it worked at a the Crown Plaza Hotel in Heathrow.

Sherrard said he had initially been sceptical about the machine but then tested it in the car park with a Lithuanian police official.

The device apparently successfully found a .22 bullet in a variety of locations from different distances.

“Each time it was amazing,” said Sherrard.

“It seemed to do what it said on the tin. It was a product I could sell. The demonstration dispelled my initial concerns over the device.”

Sherrard went on to sell dozens of the devices in the Middle East, Asia and South America.

He said that all his clients would have tested the device before they bought it and he did not have any suspicion that it did not work.

Sherrard had also been given reports on the device including one from a secret Russian laboratory which backed the device.

“The reports confirmed my own understanding of the effectiveness of the device,” he said.

He said only one customer said the machine did not work but they did not accept his offer of a full refund.

Sherrard had been selling the device for eight years when he got a letter from the Office of Fair Trading questioning him about the claims made for the Alpha 6.

He sent them a machine to test for themselves and did not suspect at all that it was faulty.

“As far as I was concerned this was something to do with my marketing,” he said.

He continued to sell the Alpha 6 and did not withdraw it until August of that year.

“My solicitor received information that it could not work and there was no way I could carry on selling it,” said Sherrard.

Sherrard denies supplying an article for use in fraud.

He is being tried alongside Sam Tree and his wife Joan, 61, who allegedly manufactured the devices at their home in Houghton Road, Dunstable. They deny making an article for use in fraud.

The trial continues.