I guess I'm wondering what the equivalent for the UK shall be? What sore of flavour text or narrative justification it might have?
What if the revolutionary socialist spirit on the Clyde had a resurgence in the 30s rather than becoming more moderate, as actually happened historically?
I think describing it in those terms really is something of a stretch. My grandfather was a communist, "radicalised" (in the modern parlance) during the 1930's, but none of them were very serious - it was very much play-acting. He would literally read the Daily Worker, agree with its editorial on the necessity of the building of the "Anti-Fascist Rampart" (AKA Berlin Wall), and then drive his Rolls-Royce to work.
We can of course play what-if, but the reality was not revolutionary.
After all, a communist uprising based in Hampshire or Kent would simply be less plausible, and thus less immersive than a similar uprising from Glasgow, purely based on the actual historical context of the time.
Hampshire or Kent perhaps not, but only because they are relatively unindustrialised (though of course, Portsmouth is in Hampshire and was a big centre for trade and Labour). However, London was a strong location for left-wing sentiment, as was a great swathe of the industrial North - particularly Tyneside.
It would take something very big to cause a civil war in the UK. A military coup (as in Spain in 1936), or a disputed election-result might do it, but there was no-one prominent in the military who would have seriously gone along with such a plan, and our electoral system makes disputed results very unlikely.