I don't believe the UK government for this matter is naive. They know very well what and why they are doing this and it's the same strategy used in different parts of the world. It's not new and there's no need to come up with anything new because it works so well and you can justify trading privacy (or even more important things) for security this way no matter how little sense this makes.

I do think that it's naive to think that one of the most important countries in the world with a rather effective intelligence service and a lot of smart people everywhere in the state is naive. I really don't think the UK government believes that if they remove encryption from popular chat apps the tiny percentage of population that might use it for evil purposes will be caught instead of, you know, moving to a different mechanism.