These networks are running at 5.8GHz without the safeguards introduced by Ofcom when the band was opened up, according to Paul Munnery, managing director of Wireless CNP, which designs and installs wireless networks.
When Ofcom made the 5.8GHz band available to use under a "light-licensing" regime in December 2003, it ruled that network equipment had to include dynamic frequency selection (DFS) technology to minimise interference with military radar, because the Ministry of Defence already used the band, and transmit power control (TPC) to ensure that a network transmitted at the lowest power level possible.
Munnery told the Wireless LAN Event in London on Tuesday that the companies using such networks without DFS and TPC could soon feel Ofcom's wrath.
"Ofcom may be about to take to task some high-profile installations that haven't complied with these two features," Munnery said.
As other governments haven't insisted that 5.8GHz networks in their regions must use DFS and TPC, a lot of equipment is available that doesn't support it. This kit is available over the Internet and from some wireless vendors in the UK, and is often significantly cheaper than authorised devices that comply with British regulations.
In some cases, a company may be running an illegal 5.8GHz network unknowingly, if they employed a third-party to install it. If caught, they could face a hefty fine.
But according to other experts familiar with the situation, Ofcom may not actually be in a position to take firm action.
"Ofcom has said it's looking to the industry for self-regulation. In practice, this means they want wireless vendors to grass each other up, because Ofcom hasn't even got the necessary equipment to find an illegal 5.8GHz network. Ofcom's equipment only goes up to one gigahertz," one informed source told ZDNet UK.
He estimated that there are "tens, if not hundreds" of illegal networks running at present, and that many of the offenders are schools, who are using 802.11a access points to connect buildings together over an outdoor link. This violates the rules on the use of the 5GHz band, as 802.11a kit should only be used for indoor use.
Ofcom has inherited an ongoing project from the Radiocommunications Agency for a chain of unattended monitoring stations (UMSs) and remote monitoring and direction-finding (RMDF) units, to be used for spectrum use monitoring and interference detection. However, the last report from 2003 said that just six RMDF units were in use, and that they covered "VHF and UHF monitoring and direction-finding". 5.8GHz is well above the 3GHz boundary between UHF and microwave.
Ofcom was not immediately available for comment.
ZDNet UK's Rupert Goodwins contributed to this report.