Just to clarify, the ID card program was terminated in 2010 with a new incoming government. It started in around 2005 or 2006.
It was effectively in two parts. One was a national identity registry, which was going to contain 140-something pieces of personal information, both biographics and biometrics. The idea was that citizens would have to enrol by providing their fingerprints, iris scans, and photos and things.
The card was going to be the physical manifestation of that register. Effectively, U.K. citizens would carry it around, and if they were challenged, the card could be checked. It could also talk to the central register and, if need be, bring back fingerprints and things, which would enable a law enforcement officer or whomever appropriate to validate that the individual in front of them was the same person who'd originally had the card issued to them.