I read these stories about the UK and I can't help but think of the latter years of the Roman Empire. Rome became dominated by people from the provinces. These people thought of themselves as Thracians, Egyptians, Macedonians etc.
Rome had lost her identity, has the UK lost its identity as well?
Disagree with your analysis of Rome. By the later Empire there was much less local feeling between the former nations and against the Empire, although there was less unity between the two halves of the Empire. Even the near neighbors felt themselves to be part of the Roman world, and tried to take refuge behind the frontiers when the alien Huns attacked them. Your idea is also disproved by the fact that the only pre-imperial nation to resume its independence was Britain, which was cut loose by Rome, rather than seizing independence.
The Empire died because its economic system, based largely on expansion to create wealth in human slaves, failed when expansion ceased. Expansion had to cease because the Empire had become impossibly large to administer. Having to expand to exist, and being too large to expand, meant that its end inevitable.