In the US, the pervasiveness of social security numbers as id makes the social security death register very useful. Sure, there may be some deaths unreported, and some reported under the wrong SSN for various reasons, but most of the time it works.

I don't think the UK has a similar enumeration of people, and then you've got data problems. Names drift over time. Name and birthdate aren't unique. People may forget their birthdate non-fradulently and use another one; people reporting the death may not have the right birthdate and guess, etc.