Part of the reason this is difficult maybe that there's an ongoing problem in the UK of foreign gangs using faked documents to steal inheritances[1][2].

I'm skeptical though whether a compulsory ID card for British nationals would help with that.

1. https://www.bbc.co.uk/mediacentre/2025/shadow-world-the-grav...

2. https://www.theabi.org.uk/news/is-eastern-european-organised...