With the bird right at the bottom of this (heavily cropped) picture, it looks an odd composition. But at the time, I had no idea what, if anything, I'd photographed.
Pigeons, small birds etc had gone up in an apparent panic. At the same time, "something" flew into the lower branches of an evergreen 60 yards away and I picked up the camera. Thought I could just make out part of a bird - maybe a Wood pigeon - and took a shot roughly in the right area. Checking the results later on the camera's back panel, in this one there appeared to be no bird. I was about to delete it, but to be sure, cleared the panel of picture information. It unexpectedly revealed this Sparrowhawk, about to fly out of the bottom of the frame. It had been completely obscured by the number of the shot overlaying it. So this was a fluke, but a nice surprise.
It looks like a juvenile, from the pale feather edges and indistinct undertail barring, and perhaps female given the absence of reddish tones. But suggestions as to age and sex welcome.