One Login is an "authentication" system, an oAuth provider with identity added on. This means you can prove your identity once (to various levels of confidence, as defined in GPG45 [1]), and use that same verification across different government services.

When people talk about a national ID system, they're often talking about some form of "authorization", i.e. proving that you are entitled to certain things.

There currently isn't a system in the UK that can definitively prove that you have access to every service. For example, even being a British citizen and having a British passport doesn't automatically entitle you to access the NHS.

[1] https://www.gov.uk/government/publications/identity-proofing...

No I get that but you could eg link your passport to the One Login and it'd make the UX much better for many services. For example, if you linked passport, driving license and NI/tax account, then I think for 99% of services you wouldn't need to fill anything in.

FWIW I was impressed with the DVLA driving license process, where you can type your passport number in and it pulls your photo from the passport. Very smooth. Could be even smoother if it could link automatically your passport.