On getting home I went on to Xeno Canto and after some searching and got a match. Icterine Warbler! So that's another occasion when I could have made a decent recording, even seen the bird, and didn't.
I've been back twice since then, and today on the second trip found a bird giving pretty much the same song at the same place. Here's a second, better recording.
Finally I located the bush the song was coming from, saw a twitch in the leaves, and there it was, a ... well the answer is at the bottom of this post.
I've spent a few hours in the Forest as you can imagine, and apart from the usual woodland birds (Nuthatch, Garden Warbler, Great-Spotted Woodpecker, Buzzard), saw Spotted Flycatcher - three minimum with at least one juvenile, and also a couple of Marsh Tits. I saw two female Purple Emperors, 7 Silver Washed Fritillaries, and some Purple Hairstreaks. I've finally got my eye in on the Hairstreake; there are often Ringlets in the higher branches of trees, but these have a leisurely flight. Hairstreaks are smaller and whizz around like mad things. I eventually got a distant picture, which is shown much blown up and cropped here.
|Purple Emperor Female|
|Purple Emperor opening its wings.|
|Great Spotted Woodpeckers having a disagreement|
|Purple Emperor sunbathing|
Oh and the mystery bird? Blackcap! I know. I'm pretty sure that was the bird that was singing. I'm still reeling.