This afternoon he napped for two hours and didn't wake up until 6.30. That means that when I took him to bed shortly before 10 he wasn't tired, and he rebelled by kicking his feet out from under the blanket and playing with a crinkly book. However, I left him and he was mostly quiet (though occasionally chatty, and we had one unusally loud "Eek" for no particular reason). He was still awake 15 minutes ago and started complaining, so he had to be calmed down. He may well still be awake now, but the fact that we didn't have actual fighting is a fairly good sign.
Edit: Well he was asleep by the time we went upstairs, but he had to be fetched out at something after 2am. And he decided it was time to get up not long after 8am. So by rights he should be a tired baby today. He certainly has a tired mummy.