Imagine it was a physical good instead. Tax havens might not be a bad example. The UK can absolutely demand that a UK citizen or corporation bring something or another back to the country, and if the laws of that other nation conflicted then it'd be "messy" but not the UK seeking to modify what is allowable on an international basis. Regardless of what happened to the item in question, the offender would be in hot water somewhere.

Extending that ever so slightly to data, Apple and friends are definitely technologically capable of moving the data from one side of the pond to the other, and they're definitely operating in both the UK and the US. Does the speed at which data travels make that more like a cyber attack from the UK on the US (infiltrating a weak link to gain unauthorized access), or is it still more like the physical good countries seem to want to regulate it as (where Apple would have to violate one or more laws)?

What I really don't like about the matter is that if you simply split Apple into two legal entities, one for the US and one for the UK, the capability of moving the data nearly for free will still exist, but that will likely thwart the backdoor in the law. That suggests something fishy going on in our definitions and intuition, and it makes me more inclined to agree with your side of things. I'm not totally sold though; I could easily have just missed the obvious paradoxes from the side I'm partially defending.