I was right to suspect Saturday's journey would not be as good as Friday's. The train got as far as Clapham Junction (not far at all) and then sat there for half an hour because of a trespasser on the line. When we finally got going and passed through Earlsfield, there was a half-naked man sat on a bench surrounded by police officers.
That was the trespasser, then. The odd thing about him was that he had a whole load of electrodes across his chest. He had either just escaped from the local mental hospital or the police were getting ready to give him electric shock therapy. Not sure which, though.