In the face of widespread opposition, the UK Government looks set to introduce a National Identity Cards scheme, which will become compulsory some time around 2012.

It will be underpinned by a National Identity Register, holding detailed biometric information for every UK citizen. This won't just be submitting a passport photo - every citizen will have to report to a testing station, sit in a cubicle, and have biometric information recorded - fingerprints, an iris scan, and a photograph.

But we aren't talking about an ordinary photograph. In the trials, volunteers were subjected to "a prolonged photograph without the flash." The computer analyses the subject's face to produce a unique mathematical algorithm. The main purpose is for immigration control - you look at a camera, which can verify you are who you say you are. So far, so good.

What has been overlooked so far is that a product called Mandrake ( http://www.tssi.co.uk/products/biometrics) can take an image from any CCTV camera, and match the people in front of the camera with a database of facial biometrics. The technology is already used in the London Borough of Newham to spot shoplifters when they enter an area ( http://www.sourceuk.net/indexf.html?00624), and it's improving all the time.

The UK already has the highest ratio of CCTV cameras to people in the world. Mandrake, together with the National Identity Database, would give police and security services the ability to identify any individual from CCTV footage without the subject even knowing it.

Ultimately, the system could be used to gather a database of every citizen's movements in and between town centres, or anywhere else state-controlled cameras are used.

Is this unlikely? In the current political climate, probably. But the minute you sit down in that booth, and submit to that facial scan, you're giving the Government your facial biometric for ever. You can never take it back - and there's no way of knowing who will be in power in 5, let alone 50 years' time.

As the company who make Mandrake are the first to point out, facial recognition is effective precisely because it is the only biometric which can be used without the subject's knowledge. Any guarantees we are given about the uses to which this information will be put are largely worthless, since any future Government could override them simply by passing an Act of Parliament.

Privacy concerns have been raised over the possibility of reading RFID tags in these cards without the holder's consent, or problems with disproportionate numbers of ethnic minority citizens being asked to produce their cards. These all pale into insignificance when compared with the potential of this CCTV threat.

It's insidious and rather distasteful - your face, a deeply personal part of your identity, becomes a government-recognised 'licence plate.' In the same way as we now receive automatic fines for speeding, completely automatic systems could be set up for minor crimes - shoplifting, walking on the grass, who knows what?

All this could happen with currently available technology - and once the information is on the database, it will inevitably be put to uses beyond those we can imagine now. People shold be aware that giving your biometric information to the state gives them the ability to track you without your knowledge; to know your previous movements when even you have long since forgotten them. It's a tool that could be highly dangerous in the wrong hands.

Can we really trust the Government not to abuse this power?