However, the CWS stressed the firm had been retained for the sole purpose of obtaining evidence against CWS controller of retail operations Allan Green and the surveillance operation had now been called off.
Mr Regan and his team claimed they were followed at the weekend while on a briefing visit to the City offices of the Sunday Telegraph. Under the caption "the surveillance cameraman who was trailing them", the newspaper carried a picture of a suspicious-looking man in a cloth cap giving the thumbs-up.
The CWS said: "He was nothing to do with us. Either there is a second party trailing him or, more likely, Mr Regan set the whole thing up to blacken our name."
The case highlights a growing use of surveillance and hi-tech spying techniques in industry and commerce. City investment banks suspect they are increasingly prey to sophisticated electronic spying gadgetry, used to collect lucrative inside information.
As industrial espionage becomes more commonplace, the market in eavesdropping and bugging equipment is booming. The following devices are among the sophisticated technology now available.
For security-conscious companies, perhaps the most worrying development on the market is laser equipment that can pick up vibrations caused by voices on a windowpane and then decode the distortions in the returning laser beam into sound. The equipment can be set up outside a building so there is no need to gain access.
Minute "pin-hole" cameras that can be disguised as wristwatches and cigarette lighters, or concealed in places as apparently innocuous as the stud on a briefcase.
Should you wish to tape a business meeting discreetly, credit card- sized cassette machines are available that can record for up to six hours on a single tape.
Those who suspect they are being secretly recorded can fight back with a device that generates "white noise", impairing the quality of the tape.