'56 is too early, given how much of east Africa was under British colonial control into the 60s, and how much of S/E Asia was still looking for independence. It's likely the population of the empire was still above 100mn at the time. I'd say '56 is more like the start of the very rapid decline of the empire.
It highlighted both to the colonised and the colonisers that the empire was way over-extended.
It highlighted both to the colonised and the colonisers that the empire was way over-extended.