@AC "compulsory database"
..." it is possible to search an entire country's population in a few seconds and find the matching ID. So it doesn't matter if you carry a physical card or not - if your biometric is in the database, then you're already carrying your card."...
Since you ask actually no, it's not like that at all. DNA, Iris and Fingerprint do not work in real life like they do in say CSI at all.
When IPS ran tests to fingerprint people for the new passports a sizable percentage did not work at all, the data gathered was not good enough to prove ID as people’s finger prints do change slightly over time and from day to day. The older you get for example the less clear your fingerprints become. Fingerprints 'work' for crimes (even in criminal law there are documented cases of people just happening to have similar prints), but they only 'work' as well as they do because you have highly trained people manually checking them...
Iris is hopeless; I don't know if you ever stood in line at Heathrow and watched the Iris machines? I have, and the only reason they are faster is so few people use them in my experience - I regularly see people having several attempts to get the thing to recognise them, and occasionally having to resort to the manual 'join the queue' option anyway - I don’t know the reason for this but according to magazine articles a few years ago they had a problem with bloodshot eyes, tired eyes and brown eyes (warning: a pinch of salt may be required there)
DNA checks are perhaps the biggest fallacy here - they are widely believed to be unique per person (since your DNA is) and you are widely supposed to be able to take a blood sample and from this and a DNA library get straight to the killer... Not in real life, in real life your entire DNA sequence is not stored (it's huge). Instead they only store representative markers, small snapshots of certain areas of your DNA, of which I believe there are only 1million possible combinations. That's if the DNA sample is perfect, the sun is shining and everything goes perfectly. In reality it’s a chemical process and you get less reliability
So even if you did give your perfect DNA sample, have it perfectly analyzed and stored and have it perfectly matched it would still only narrow you down to 1 in 60 people in the UK population
Anyway that was a bit more than I was intending to type but that's why cards are still required - it’s also why the idea of using biometrics on a database to solve crimes is a dangerous fallacy at best
Hope it helps