It's highly likely that I lit on After the Party because of the author's name: Cressida Connolly. I've since discovered her father was the critic Cyril Connolly*, hence her literary name. Anyway, it's about British fascists just before WWII, but even more, how easy it is to take a small step that leads to another small step that eventually immerses you way over your head. So well written.
* Young writers if they are to mature require a period of between three and seven years in which to live down their promise. Promise is like the mediaeval hangman who after settling the noose, pushed his victim off the platform and jumped on his back, his weight acting a drop while his jockeying arms prevented the unfortunate from loosening the rope. When he judged him dead he dropped to the ground.
~ Cyril Connolly, from Enemies of Promise.