I'm aware there was decent support for socialism, especially in the British working classes in Sheffield and Birmingham, and as many of the workers bore the brunt of the war costs I was wondering if it was ever realistic that a western government, such as that of Britain, France, Belgium, or the Weimar Republic could be toppled by Communists.
As for a revolution I mean any rebellion that would get rid of the Government at the time and replace it with a Communist one.
Yes, Spain got close a few times. France and Italy had fairly large Communist factions but not nearly enough to think a revolution was possible.
Here's a link if you want some further reading.
In Bavaria, it actually succeeded, albeit not for a long while.