I mean really.
We know that the primary purpose of the modern Nation State is to maintain favorable and stable economic conditions. This is why devolution has been a long and torturous process and why Westminster wants to avoid Scotland seceding. The results may not be that destabilizing anyway in the long term, so they might just let it happen anyway. Same goes for Wales, the poorest part of the UK incidentally.
But do you really contest that if random cities and smaller units started to secede, radically shaking up the status quo and causing massive amounts of logistical, regulatory and practical confusion, action wouldn't be taken to stop that?
Throw in things like the military, nuclear power stations, nuclear missile silos and so forth, and you've got all of that to deal with as well as the question of taxation.
Really? You think that this sort of thing would be received with better grace than the Middle East has shown? Really?