Read my timeline Dead By Dawn. British Civil War between the Conservatives, backed by King Edward and the military, and the National Socialist-Labour Government, backed by the Soviets and the French.
The Irish crisis of 1914 had the potential to flare into a constitutional breakdown. A significant part of the Army was ready to mutiny rather than enforce Home Rule on Ulster.
Some Tories were prepared to support the Army dissidents against the government...
I guess if some authoritarian aspects of the Conservative and Liberal parties decided to ban working class parties, then maybe that would encourage a socialist uprising at some point.
unless abdication or refusal to abdicate by Edward over the the whole Wallis Simpson thing brings about some kind of constitutional collapse and Moseley and the BUF take advantage of that and their coup is then aided by European fasicists and changing the face of 1940s europe totally ...
As some people have stated: Ireland, the General Strike or a combination of both (an Irish crisis happening at the same time as the General Strike) are the most likely PoDs.