I don't see why they can't just connect a driving licence and your details the same way California does. In Calif you are required to carry a picture ID which is your licence or personal ID issued by the DMV after the age of 18. Here in the UK you can get the same but you are not required to carry it with you which I think is sill in the first place. They could connect the two but instead seem to just want to make more money on a sill scheme.
The thing is, though, that in this country one cannot take out a driving licence (other than a Provisional one) until one has passed a test. No test pass, no licence. There are plenty of people who never learn to drive because they live where public transport is easier (London is an obvious example).
Some people don't even have an NHS card, because they have never registered with a doctor - and those who have never worked, or registered for unemployment benefit, wouldn't have a National Insurance number. Whichever system we look at, there are always going to be some who are not on that system.
I'm not saying I'm in favour of a compulsory card for 100% of the population - I'm dead against it. (How stupid do they think terrorists are, not to be able to come up with their own ID cards? And if, as so far, they are, up until the day itself, apparently perfectly ordinary British citizens, they would end up with an ID card anyway - it doesn't say "Terrorist" on it!) I'm just trying to highlight the difficulties with trying to tag an ID card onto any existing system.