With a PoD anywhere between its foundation to the present day, make the Monster Raving Loony Party gain, and hold, seats in the House of Commons. It does not matter whether those seats were gained in a general or by-election.
Didn't we have a TL where the SDP-Liberal Alliance won the 1983 GE, instituted PR (or some such electoral system) leading to the Loonies picking up the last seat on preferences?
That was my TL "Clustershag To Ten Downing Street" though I would take the whole thing with a pinch of salt. I had A county wide constituency (I think, its been a while) with Melody "Boney Maroney" getting in, essentially due to protest votes against William Hague/The Tory govt.
Will read that in due course. It was another TL, with Paul Simon as US President in 1988 and I think it was Howling Laud Hope who was the one who became an MP.