Re: "no requirement of 'registration' for deactivated firearms"
>Might as well impose ID cards.
You've got them. They look like a driving license.
People in the US have the same attitude to ID cards as those in the UK but the country really needs a form of ID so the "RealID" law was passed years ago. This gradually introduced changes to states' driver;s licenses that meant that getting a RealID compliant license requires the same sort of ID and citizenship checks you'd need to get a passport. You can still drive with a non-RealID compliant license but soon you'll be restricted in what you can use it for such as use air travel. (It also marks you as 'somewhat suspect' to law enforcement.)
UK licenses may have a way to go to get to this state but as the DVLC system is already tied into the passport database it may not be necessary. I can't speak for modern England but years ago one of the signature features of living there is nobody carried any ID ...... but at the same time the police always seemed to know who you were. ("Think About It".)
Back to the topic. You really, really, do not want the same level of gun ownership in the UK as we have here in the US. Even deactivated guns. As for EU directives, it seems that only the UK slavishly follows Brussels's diktats. Think of them more as 'guidelines'.