That is to say it was a merlin if I got it right as it wasn't hanging around for an identity parade, but I know sparrowhawks and kestrels well enough to be confident. The only area of doubt was that I perceived it to have a pale rump, but it may be I was seeing the side of its underbody as it flashed through the air. So that was a birdwatching first even if the brevity made it hard to get unduly excited.
Most other anglers seemed to struggle on the day. On reflection it was a day for smaller baits and finer tackle, so my approach was too crude. But I had a strong feeling that the presence of groats in the swim attracted barbel. The other learning point was that I must face up to the fact that I need to try much larger hooks when fishing meat. The meat was working in the last couple of hours but the bites were lightning fast and the hook always came back bare.