Hi.
Well the Nightingale song is great. Very unmistakanle once learnt and very powerfull sounding. But I have heard people identifying both Blackcap and Garden Warbler songs as nightingale. Especially more so of garden warbler as it will sing from deep cover sometimes like the Nightingale. I've also seen people identify a garden warbler as a nightingale.
These were taken on Sunday. This was one of three birds, two of which were singing. Took about an hour before it was visible enough to get a picture. Went back again today and still two singing but a lot further apart now.
Hope this helps,
Cheers David