[neonemesis]

The new joint service doesn't have any hope of getting devolved government in the UK correct. Eg. Steve Barclay is the Health Secretary for England, not the UK Health Secretary, but you can guarantee that he'll be wrongly referred to as the UK Health Secretary.
Same goes for Education Secretary, Transport Secretary, and any area of government that's devolved to Scotland, Wales & NI, who all have their own ministers responsible for these areas of devolved government.

But the News Channel couldn't even get devolution right when it was just broadcasting in the UK, so trying to explain the UK complicated system of devolved government to the rest of the world.............

I don't see why they can't get it right - it would also benefit domestic viewers if Steve Barclay was referred to as "England's Health Secretary".

That said, I do wonder why they treat viewers like they don't have access to google and can't look up something they don't understand (like Chancellor of the Exchequer). CNN doesn't seem to have this problem when it comes to US officials.

Not quite that simple. In the Barclay example he is a Secretary of State within the UK Government. A member of the Cabinet of the UK Government. There is no English government or ministerial roles defined for England, even though that is the extent of his territorial jurisdiction. So it can be argued that it is legitimate (albeit unhelpfully vague) to refer to him as the UK Health Secretary.