Picture posting is enabled for all :)
Well, it would actually pass muster as a nightingale. Can you describe the song - nightingales aren't easily mistaken for anything else once you've heard one - trilling, liquid song, like a thrush but more so - and loud! Thing is you don't tend to see the bird, only hear it singing from scrub. Where and when did you see it?
Looks like a warbler, and Willow or Garden are my guesses, based on having a warbler-like song...Chiffchaffs are very common but don't really warble, just shout ;D.If it was a reasonably short, descending song with a little flourish at the end, Willow Warbler.