From a poll supervisor point of view it's not as "nuanced" as you may think. It's very clear that political campaigning including material that identifies candidates, parties, or political positions are not permitted at the polling place. "Place" does not mean just the room in which you find the ballot boxes et al, it extends to the exterior of the building (while that may be vague, show me the place and I'll show you the perimeter at which I won't object to your demonstration). Any activity that inhibits the process of voting or access to the polling place, inside the polling place or outside is not permitted even if that numpty's position has nothing to do with a particular party or candidate who is running.