Evidence of firms snooping on employees will be revealed today at a special conference organised by the MSF trade union - opposite the MI6 headquarters on the river Thames.
"All employees should be aware that Big Brother is already watching you," said the MSF's general secretary, Roger Lyons. Simon Davies, from the London School of Economics' computer security research centre, said: "In the UK, employers can tap phones, read e-mail and monitor computer screens. They can bug conversations, analyse computer and keyboard work, peer through CCTV cameras, use tracking technology to monitor personal movements, analyse urine to detect drug use, and demand the disclosure of intimate personal data."
Mr Davies says that firms often justify surveillance on the grounds of health and safety, customer relations or legal obligations. "The real purpose of most surveillance, however, is for performance monitoring, personnel surveillance, or outright discrimination."
Guy Dehn, of Public Concern at Work, said that calls to their helpline showed that surveillance is a growing problem. "Several people have contacted us to say that they have found video cameras hidden in smoke detectors. These discoveries antagonise employees and undermine any sense of trust in the workplace," says Mr Dehn.
The intrusive technology available to companies is remarkable. A Japanese company has designed a toilet that can be used to analyse employee's urine for drug or alcohol abuse.
According to the LSE's Simon Davies, a new software package, The Ascentor, can scan e-mails and decide whether a message appears to be about legitimate company business. Companies are increasingly restrictive about employees' use of computer systems for personal use. Last week a Cheshire woman who had used the company computer to surf the Internet for a holiday package lost her case for unfair dismissal.
At Rolls Royce in Bristol a employee inadvertently sent an "inappropriate image" - pornography - to the wrong colleague, who then complained. A company investigation revealed an e-mail network on the company system used for conveying risque material and jokes. Last month 15 people faced disciplinary hearings. Five were sacked and others were given written warnings.
According to Robin Chater, of the Personnel Policy Research Unit, many City institutions keep a close watch on their employees using the new techniques. "Merchant banks monitor their staff's communications more closely than just about anyone else. This is the `Leeson effect' - they are terrified that an employee might make unauthorised financial transactions."
The Data Protection Registrar, Elizabeth France, who will address today's conference. said: "The increasing use of surveillance in the workplace has significant implications for individual privacy." She said she would be publishing guidelines "which we hope will set out clear ground rules that will make sure employees are treated fairly".
Secret Surveillance at Work
n Leeds Metropolitan University used cameras secretly to film and record the conversations of three staff members who had been the subject of anonymous allegations of drug dealing. The three men only found out about the surveillance after they had been suspended from work. No evidence was found of drug dealing.
n Birmingham City Council bought pounds 60,000 worth of spy cameras and other equipment earlier this year. Unions threatened industrial action after the council used it to film and eavesdrop on employee conversations. "This is the day of Big Brother," said Steve Foster, chairman of the council's trade union group.
n Brian Harris, a representative of the MSF union at the former Siemens Defence Systems factory on the Isle of Wight, discovered that the company had hired private detectives to conduct video surveillance on him. He reached an out-of-court settlement after filing a legal claim aagainst the company.