A letter to the editor of the Daily Telegraph, from Dr Chris Williams, European Centre for the Study of Policing, Open University, Milton Keynes:

One problem with the proposal for a national ID card (News, Apr 27) is the security of the information in its "clean" database.

Although police all sign the Official Secrets Act, and are well paid, well supervised and largely trustworthy, at least one policeman has been sent to prison for selling the information on the Police National Computer to the highest bidder - in this case, credit reference agencies. HM Inspectorate of Constabulary recorded their concern over this practice in 1999 and recommended measures to stop it, yet the Police Complaints Commission admitted in 2002 that "there will always be a few officers willing to risk their careers by obtaining data improperly".

So we can't trust the police to keep a sensitive database watertight. Can we trust other state institutions or outsourcing companies such as Capita? To be usable, an ID card database has to be accessible by hundreds of thousands of people. And the security has to be permanent.

In 1938, the Gestapo took over the files of Interpol's predecessor when they entered Vienna. If we put all our data eggs in one basket, we need to be certain that a DVD with all our details on it never gets to al-Qa'eda, the IRA or the unknown evils that the future doubtless holds.