System manages to already be broken before implementation starts
And the existing digital ID system GOV.UK One https://signin.account.gov.uk/sign-in-or-create is almost unusable even though hardly anyone has to use it. Of the 4 people I know who attempted sign-up and identity verification, only 2 have managed it so far. Help pages and telephone support are, of course, unusable or unavailable. And this only needs to be used by a fairly small number of people - less than a million I believe (people who have to file company information and some others).
Imagine what would happen if 60+ million people all had to sign up to the eventual national ID solution over the course of (say) a year?