Earlier quoted context omitted.
If apple's UK iPhone profits really are in the c. 50mil range, then a (5 to 10)bn fee to remain is commercially non-viable. Note that this is about Apple's ability to sell an iPhone in the UK, and as far as I can see, it wouldnt affect whether the entire company would remain in the UK. If I were apple, I would withdraw a product from a country which supported this kind of racketeering.
Leaving the UK market won't save them licence fees. They've already been incurred. It would be less like relatiation, more like flouncing off in a huff.
They haven't paid them yet. And if they leave the market, they have no reason to pay it.