In 2004 the warning from the UK's data protection commissioner, Richard Thomas, that Britain was "sleepwalking into a surveillance society", acted as a wake-up call on the issue but has not prevented it from happening. Advances in technology mean that CCTV cameras follow us as we walk down the street. Every time we make a phone call, pay for an item with a store card or visit a doctor, our transactions are tracked, our preferences recorded. Every day each of us leaves a trail of electronic footprints that has the potential to build up a detailed picture of who we are and what we do. Because of the security threat facing Britain, the public is prepared to accept greater intrusion by the state into our private lives. For example, there was little criticism when it was revealed that number-plate recognition technology may be shared with police investigating terrorist suspects, and many regard CCTV as more reassuring than intrusive. After all, the old argument goes, if you have done nothing wrong, you have nothing to fear.

This assumption is both naive and misguided, especially when confidential personal data harvested from both public and private sources can be pooled and shared without an individual's knowledge. Today Mr Thomas warns that an increasingly sophisticated web of information is undermining the individual's right to privacy. We already have a situation in which the government and its agencies can tap into sources as diverse as the DVLA, TV licence records and London's Oyster card and congestion charge payments systems. Simultaneously, commercial logic is driving companies to trade personal minutiae about customers, so that they can bombard them with increasingly sophisticated and personalised marketing. Even companies that do not routinely share information with third parties may be required to do so by law in certain circumstances.

It is time to challenge this trend. There are legitimate concerns about the quality and security of the data held on these databases. Incorrect or insecure information can lead to credit being refused or identities being stolen. It is wrong that detailed information about our lives and habits can be sold without our consent from one company to another for commercial gain. Such information should be ours to give away, not for the state (or some department store or grocer) to requisition.

Some data-sharing is sensible. A peripatetic teacher working in five local authority areas should not be required to obtain disclosure clearance in quintuplicet. An elderly person moving into residential care should not need to provide identical information to five government departments. The challenge for government is to distinguish between sensible information-sharing and Big Brother intrusion. It is surely a sign of ill-health in a democracy when citizens lose control over the way their daily lives are monitored for commercial or political ends.