It could be a great idea to have a central ID, even if it was just for convenience, I like many have all sort's of stuff in my wallet, a passport, driving licence, tacho and cpc cards, nhs card, bank cards, and all sorts of other things that could possibly be consolidated into one form of identification.
If it was honestly just for identification purposes it would be great, the problem is, like many things in our world, if it can be abused, it probably will be abused, some way or another.
One of the reasons behind the push for a digital ID seem like a total waste of time, it will not ever stop illegal working in the UK. You only have to go to some of your local pubs, clubs and fast food restaurants to see illegal workers first hand.