Foul play as bug found hidden in Mourinho's favourite restaurant

Ashley Cole's move to Chelsea has already been compared with the sort of cloak-and-dagger defection in a James Bond spy thriller. But the plot is about to thicken. One of Jose Mourinho's favourite restaurants - where the England footballer's escape from Arsenal is said to have been plotted - has hired a counter-intelligence firm to review security after bugging equipment was discovered in its dining room.

Portal, a Portugese restaurant in the City of London, is to pay agents from the International Corporate Protection (ICP) Group to make regular "sweeps" of the premises to protect the privacy of its high-rolling clients.

The move follows an incident in which kitchen staff discovered a surveillance device in a plug fitting near to one of the restaurant's discreet corner tables, where several members of the Chelsea team recently dined.

"We couldn't believe it," said Portal's owner, Antonio Correia. "A fortnight ago, I bought a radio for my staff, so they could to listen to music in the kitchen while they were working. It produced terrible feedback, and on one frequency we could hear what was being said near to the serving hatch."

After searching the premises, Mr Correia found that a device in a two-socket adaptor was responsible for broadcasting the sounds. Although ICP did not find further bugs, the firm has now been employed on a rolling contract.

The restaurant, which includes several private rooms, says the device was discovered less than 24 hours after it had been planted. The celebrity and corporate clients who tuck into its Iberian cuisine make it a prime target for covert surveillance operations.

As well as hosting lunches and meetings for City firms, Portal is a favourite of the Chelsea camp, and it was named by Mourinho, the team manager, in a Time Out interview as one of his favourite London restaurants.

Mr Correia said: "Who knows if the device was connected to them [Chelsea players]. To me, it doesn't matter: a lot of my clients work at the Stock Exchange, or for finance companies and lawyers. They are people who take privacy seriously, so it is very important for me as a businessman to protect them."

Although Portal is thought to be the first restaurant in Britain to employ a firm of spooks, the practice is relatively commonplace on Wall Street, where industrial espionage is treated as an everyday corporate hazard.

In a recent high-profile case, three New York-based former employees of Coca-Cola were charged with stealing trade secrets, after allegedly attempting to sell the firm's secret recipes to its arch-rival Pepsi.

"To be honest, I'm surprised that we haven't been asked to look at a restaurant in the UK before," said ICP's director Will Geddes.

"Counter-surveillance has now become so widespread that most of our work is actually training people on how to find devices, since most companies have taken the job in-house."

"I can't say exactly how often we will now be checking the place, as that will compromise security. But there will be regular visits by our staff."

Bugging is officially illegal, although few cases are ever bought to court in the UK. The equipment found at Portal is described as a "basic off-the-shelf device," which ran on mains electricity and, according to staff, had not been present the previous day.

"It would have required the eavesdropper to be sitting near by, perhaps with a receiver and recording device," added Geddes. "Who knows why it was there. It could have been as simple as a wife checking on a husband, but there could obviously also be a more sinister explanation for its appearance."