Jim McCormick, 57, faces a substantial prison term for fraud, the Evening Standard reported. Investigators said he made millions of dollars selling useless detectors for as much as 27,000 pounds ($40,000) each, with customers that included the Iraqi military.
McCormick is scheduled to be sentenced May 2 at the Old Bailey in London. He could also have his fortune confiscated.
Trial witnesses included Belgian Police Superintendent Theiry Meunier, who described his experience with one of McCormick's devices.
"It was not only the cheapest machine, it was the only machine," Meunier said. "We had no results from it. We tried to use the device for detecting drugs in cars for several months. We also provided the detector to detectives seeking to detect drugs. The results again were negative."
McCormick, who lives in the Bath area, went on trial in March after a three-year investigation by Avon and Somerset police.
Investigators said he put lives at risk by selling a device that might give security officers a false sense of confidence.
While McCormick has continued to maintain his devices do the job they were supposed to, police, prosecutors and unhappy customers say they are simply golf-ball detectors given a fancy look and fancy marketing.