Re: What do they expect?
Paper can also be forged or lost/stolen in exactly the same way as [badly designed/implemented] digital IDs can.
Yes: If the main service goes down, then a digital ID can't be checked, but if a paper ID requires the checker to know what a fake looks like (instead of having a strong authentication method to verify the user) how reliable is that at identifying a person?
Let's be honest here, digital IDs are the future but their use is based on having a good set of use cases, a solid, SECURE design and a well implemented (and secure) delivery. In the case of the UK, I think that it needs also to have a really honest and persuasive way of communicating why it is a good idea. No one has done that last bit yet and the use cases all seem disjointed, isolated and badly communicated..
I'm also going to say that, with the current crop of main consultancies (Crapita, Fujitsu, etc) having a solid, secure design and implementation is likely going to be a challenge.