I've been thinking about this and I think it has a lot to do with the way UK people see the US and want to copy it. When fascism rises over there, it also rises over here; when it falls over there, it falls over here.
Tom Nichols pointed out that we are in an age of incumbent disadvantage: the party in power is, instead of being more likely to be elected, now held to blame for the ills of the world and becomes less likely to be reelected. This is true not only of parties but seemingly of ideologies as a whole.
As such, I think UK fascism is suffering from the fact that fascism is in power in the US, and therefore has the incumbent disadvantage effect even though they're not in power here.