Stuck on SE corner.
15d) Need tips for this. Latin phrase maybe? Congress = sexual act?
8d) I have the first word. Need clues for the second word, which I assume ends in G-E.
15 isn't Latin. It's a very clever "hidden". You are correct on "Congress"!
8d not G-E. It's misleading, as the PM wasn't a Conservative (the latter provides something else).
21d and 26a are bamboozling me. Can't get one without the other. I'm hung up on the last 5 letters of 26a being a Chubby Checker move. Just a parsing hint would be welcome.