What set of circumstances would it require for there to be an armed revolution, or outright civil war in the UK ? preferably after WW2 though anytime after WW1 is still fine.
You'd probably need a scenario similar to The War Game where a limited Nuclear War leaves large swathes of the population alive but not enough infrastructure to support them.
rebellion in Britain after Britan declares war on Germany in 1939.
Ordinary people say never again.
The last was was to be the one that ended all wars.
We will not fight in the trench of France for 4 years like last time while war profiteers become rich.
We want peace and we want it now.