Immigration, Asylum and Nationality Bill

I understand that for the time being, ID cards will be voluntary. The only documentation with which an individual could confirm his identity would be a passport. I see no reason why a copy of such a document could not be handed to the individual to establish his identity in terms of facilities, doctors, schools, or whatever. That would be helpful. There seems to be some resistance to providing a copy, particularly given Andy Burnham’s comments in the other place. What is the logic behind that?