On a related note, they built their digital ID so that third parties could verify attributes (it's NOT just a single-service login across government + a linking ID across government services, which is how it was sold by the BBC).
They're pretty close to completely de-anonymising the internet for UK citizens. Say they introduce an Australian-style social media ban for under 16s, then requires all social media to link their accounts to digital IDs for this verification.
Naturally the only remaining loophole is if a UK citizen manages to avoid being flagged as British ever by using a VPN, so I expect they will focus on that going forwards. Keep in mind the UK already arrests and imprisons vast numbers of people for speech offences, there's no slippery-slope argument here because the UK is already at the bottom of the slope as an ultra-authoratitarian anti-speech nation.