Of course, individual liberty is something that we should all be privy too, but the state must go to some lengths to ensure that the liberty, to all and intense of purposes is maintained.
Whilst Alex's articulate argument has some solid foundations, it may have skirted or side-stepped some issues.
Firstly let us not look on the ID card as ONLY a proposed deterrent against terrorism. Is this the only crime in the UK that we should be vigilant against? Think of the number of crimes that happen within the UK that don't make international or even national headlines. Gangland or racial attacks etc. The family of a person killed in a terrorist attack would make headlines, however a person killed in a drunken brawl would make fish and chip wrapping. What's the difference to the families involved?...None
Terrorism, granted is a more global and widespread threat, however these street crimes are rising at an alarming rate.
From an administrative point of view then yes, it would be an expensive cost, but you don't get anything for nothing. Of course, it would have to be a complex system but in a society of ever advancing technology, this would hardly be a groundbreaking feat, at least not for long.
We put our faith in these systems already. Are we paying the right amount of income tax and NI contributions, is our council tax up to date, has a work visa expired, are we receiving the correct pension benefits? These are all systems that could break down.
Finally, yes this is the state infringing on our rights. But if all it takes is for the state to run through my details for a milli-second in an attempt to locate a criminal then I am happy for them to do so. Let's face it, if you have nothing to hide then you won't even be aware it's taking place and the long term results in policing crime would be dramatically reduced.
Let's take care of crime on our doorstep first, then we are in a better position to deal with more widespread issues.