The polls will open at just about the time I'm posting this. Your "election" is just about as rational as, well, the ones we former colonies have.
Vote your conscience; but your conscience needs to include "tactical voting if necessary to keep The Enemy out of Number 10." For me — and probably for anyone reading this blawg — The Enemy is Boris the Spider. For others it might be Can't-Bring-Himself-to-Reject-Antisemitism-in-Party-Activists Jeremy. And so on. Remember: This is not a single-issue election… except that it is, because one party (the Tories) is living half a century in the past:
Well I think they should attack the lower classes, first with bombs, and rockets destroying their homes, and then when they run helpless into the streets, mowing them down with machine guns. And then of course, releasing the vultures. I know these views aren't popular, but I have never courted popularity.
Man's Crisis of Identity in the Latter Half of the Twentieth Century, Monty Python's Flying Circus (16 Nov 1969). The irony of some of John Cleese's own insensitivity to others in recent statements is perhaps too much for a nominally Python-worshipping nation. But you still need to make your vote matter, and it will only do so if you cast it, even if you live in Dunny-on-the-Wold (before Edmund Blackadder becomes your local returns officer).
Come to think of it, you'd probably be better off with Baldrick as PM than any of the "realistic" candidates.