A man was fined yesterday for selling illegal devices, during a trade fair at the National Exhibition Centre, designed to block mobile phone and CCTV signals.
Dennis Huang, believed to be a Taiwanese national, was selling the equipment on a stall at a security fair on May 16.
Officers from the telecommunications watchdog Ofcom arrested him after a tip-off that he was trading in illegal equipment.
The jammers, banned in the UK, are usually smuggled in from countries where they are not illegal.
Huang pleaded guilty at Solihull Magistrates' Court to selling non-compliant electronic devices, an offence under section 13 of the 1949 Wireless Telegraphy Act.
He was fined £2,000 and ordered to pay £2,000 costs.
A spokesman for Ofcom yesterday said the equipment had proliferated over the past five years, but it was still relatively rare to find CCTV jamming equipment. The arrest was the first of its type Ofcom had made this year.
The devices emit "white noise" in the radio spectrum that CCTV and mobile phones operate at, blocking everything else at that frequency in the area. The mobile-phone jammer is commonly used to block signals in trains or in cinemas, when users' noise was perceived as a nuisance. The Ofcom spokesman said cinema managers sometimes employed them unaware that what they were doing was illegal, in which case they would receive a warning from Ofcom.
The CCTV signal jammer was thought to have more sinister usages. "I can't think of any legal reason you would use a device to block CCTV signals, but I can think of many illegal reasons," said the spokesman.
Mobile-phone jammers sell for about £200 on the internet and are the size of an ordinary mobile phone.
"We don't make many arrests because we have limited means, and this is why we are so pleased with the outcome of this case, " added the spokesman.
He appealed for any member of the public who had knowledge of where such devices were being sold to contact the Ofcom office.
A spokeswoman for the NEC said: "The NEC group security assisted the authorities investigating the situation."