Pretty sure I heard a nightingale singing in the woods behind the house just now. It sang for about five minutes and has now stopped. It was singing long enough for me to find a recording on Youtube, and also an audio file on the RSPB website, and I was able to listen to the recordings through the headphones while I could still hear the bird outside through the open window.
According to the distribution map on the RSPB site, they are not generally found in Wales, but this has been a warm summer and perhaps they have made it a bit further North and West than is usual. Also, the RSPB says they sing until early June and leave in July. So I could be imagining all this. But it's a very distinctive song, and it sounded like nothing else we have round here.
I have only heard one once before, in the South of France on a summer's evening. It's magical.