> If they arrived here legally won't they have a passport? Or national photo ID at the very least? If they are driving for Uber or deliveroo then they'll have a driver's license too? If they don't have either (or a UK birth certificate) then it's safe to say they're not a legit citizen?
Simple. Overstaying or/and expired passport will lead to that. Valid status is not a fixed binary state. It is better described as a function of personal id, rights docs and current time. Currently, the checks are more akin to updating a Boolean column on rare occasions. Digital id countries do checks more like function calls that you can perform easily and quickly
