A new report into the likelihood of ID cards being a successful anti-terrorism measure concludes that they would have no effect in the majority of cases.
Yesterday the home secretary, David Blunkett, finally published his draft bill on identity cards, which would allow a national register of identity with a decision to make individual biometric cards mandatory by 2013.
But in a study to coincide with the publication of the draft, the London-based human rights group Privacy International found that here was "almost no empirical research ... to clearly establish how identity tokens can be used as a means of preventing terrorism".
The group's director, Simon Davies, said: "While a link between identity cards and anti-terrorism is frequently suggested, the connection appears to be largely intuitive.
"Our report examines the actual evidence, and finds that the likelihood of an ID card preventing a terrorist attack are virtually zero."
Launching the scheme yesterday - a development on his concept of "entitlement cards" two years ago - Mr Blunkett said: "The primary reason for having ID cards is not because we believe they will stop terrorists. It will contribute towards the overall task of prevention, but it will not guarantee that we will not be hit.
"It can't but it will make a big difference to the operation of anti-terrorism and the security services."
The PI report, entitled "Mistaken Identity: Exploring the Relationship Between National Identity Cards & the Prevention of Terrorism", found that almost two thirds of known terrorists operate under their true identity.
The remainder use forgeries or impersonation to create fake identities, and the report says that hi-quality ID cards would still prove forgeable and so "provide a measure of improved legitimacy for these people".
Looking at terrorist incidents since 1986, the report finds that of the 25 countries most affected, 80% already had national identity cards, one-third of which incorporate biometrics.
Additionally, it found that in the most high-profile al-Qaida attacks, terrorist either moved across borders using tourist visas (in the case of September 11), or were already domiciled in the country and equipped with legitimate ID cards (the Madrid train bombings).
The report concludes: "At a theoretical level, a national identity card as outlined by the UK government could only assist anti-terrorism efforts if it was used by a terrorist who was eligible and willing to register for one, if the person was using their true identity, and if intelligence data could be connected to that identity."
The report makes no mention of the other factors the government puts forward to argue its case for a national card - curbing illegal immigration and clandestine working, and reserving social services and the NHS for those entitled to use them.
Yesterday's plan for an ID card is not the first time the idea has been mooted. Ironically, considering he was later one of the cabinet ministers rumoured to have doubts about Mr Blunkett's plan, the concept was first raised by Labour in 1998, when Jack Straw was home secretary.
He was persuaded against the idea, instead using the money to finance an extra 5,000 police.
John Major was also keen on the idea of a identity card, issuing a consultation paper on the idea in 1995, but later dropped the idea.