A Big Brother network of hidden scanners is monitoring hundreds of thousands of Britons without their knowledge, it emerged yesterday.

Scientists track people walking around cities, using the Bluetooth signals from their mobiles, laptops and handheld computers.

Scanners in bars, offices and universities register nearby Bluetooth devices and send the information to a central database.

The Cityware project, which is funded by £1.2million of taxpayer's money, started in Bath three years ago and is designed to chart how pedestrians use city centres.

It will be used to improve their design, learn how people use public transport and shops and work out how epidemics can spread.

There are thousands of scanners globally, of which 1,000 are actively tracking passers-by at any one time. Three-thousand people in Bath were monitored in one weekend alone.

Privacy campaigners fear the scanners have echoes of the Will Smith thriller Enemy of the State

The scientists behind Cityware deny they are intruding on privacy, despite growing concerns over Britain's surveillance society.

They say the signals they get from phones and laptops do not reveal personal information. But critics say the signals can contain the owner's details.

Bluetooth devices use radio signals to communicate with each other.

Thousands of people in Bath are unaware their movements may have been tracked through their bluetooth mobiles

If Bluetooth is switched on, a gadget will broadcast its name and ID number to anyone within 100 yards.

The name can be changed by the owner and often includes their own name, email address or phone number.

The scanners convert the data into maps showing the movement of people over time.

Bath MP Don Foster said: 'This is another infringement of our civil liberties and another step closer to the Big Brother state.

'We need a guarantee that all data is made anonymous before it is analysed.'

Simon Davies, of human rights watchdog Privacy International, said: 'This could become the CCTV of the mobile industry.

'It would not take much to make this a surveillance infrastructure over which we have no control.'

Bath University academic Eamon O'Neill, director of Cityware, said: 'We are recording only radio signals that are publicly available.

'We don't know who is carrying the phone.'