A few days ago, Pip, who's moored in Widbrook Woods three miles away upriver, messaged me to ask if I could identify this bird that was calling outside her boat. I couldn't; it sounds sort-of tawny owl-ish, but different to the usual to-whoo..... tut-tuddly-hoo that they do.
Two nights later I heard the very same sound here, around midnight. And posting this recording on Facebook, Liz Brownlee, over in Chew Magna, said she'd heard a similar sound.
So for want of a better ID, it seems to be a call peculiar to tawny owls at this time of year; maybe a courtship thing.