However, as I say, ID cards have other benefits. You could have just one number for National Insurance, NHS number, passport, driving licence number, library card, so on and so on. It would just make life so much easier.
Most illegal immigrants already have a false passport and other documents - or more than one - probably before they enter the country - so there is no reason a small industry providing false ID cards wouldn't spring up. If the technology existed to link the cards to DNA samples or whatever they do, that might be different and prevent duplication. It would not stop the fraudulent aquisition of a card though.
The first thing that is needed is an end to the "thought police" attitude and to firm up border controls and immigration policy, and to not be afraid to sort out fraudulent benefits claimants and those who are not entitled to be here.