Offline fallback required
If central government plans that everybody should be using this system to access their online services eventually, then an offline registration process is definitely going to be required for those people who have an insufficient credit trail. Perhaps the Post Office could get in on the act here, offering a document examining service in the local branch to those people who cannot, for whatever reason, be verified online. I would have thought that things like passports, driving licences, council tax bills, bank cards, etc , would be sufficient if presented by the applicant in person. My experience of the main credit reference agencies is one of incomplete or just plain incorrect information held on my record and getting them to correct/amend it is a triumph of perseverance. I would be very surprised if I was to pass an online check, even though I have lived in the UK for all of my adult life.
I hope the problems of this new ID verification service are ironed out in the near future, for if not, I can see the age old demand for National identity cards rearing it's head again.