Don't get me started on the UK and the ID card. It's stupidity at the highest level. There is a de-facto "ID", your national insurance number (like a social security number). Except it has no ID features, and cannot be changed. So much, much worse than an ID card. As far as practical ID for bars/clubs, people usually just use a driving license, or are forced to use a passport. Complete idiocy.

(However to get back onto topic, most people in the UK will have a passport, otherwise they should have a NINo allocated at birth. For the people who have neither, the GDPR is the least of their worries.)