UKC

Sorry for the terrible photo! Taken with my phone at full zoom, then put the contrast on full to try and get any colours, but no joy.

it was hopping around in the foliage at the top of a small tree on urban wasteland and singing; song similar to a Black Redstart but without the scratchy bits. I caught several flashes of white on a dark body, but the song definitely wasn‘t a pied flycatcher. Slightly smaller than a sparrow, and thinner; beak definitely insect eater. Any suggestions?

Hope this isnt a way to "cheat" on 'birdle game uk'.... 👀😆

Blackcap?

No, the song was way different, not nearly as varied, but thanks!

I presume you didn't have the Merlin app to catch the song.

Two "combined thoughts - first one is Common Redstart (edit: doesn't look right even if leucistic), second one is maybe it was a leucistic individual (whether Redstart or not), that would certainly confuse matters.

My instant reaction without reading anything was blackcap. 

Couldn't be a nuthatch could it?  Maybe one with a bit whiter belly and darker back than average? 

It's the 'beak in the air' posture in the pic that has me thinking that, and this version of the song seems to fit your description:  https://macaulaylibrary.org/asset/305397

Coming round to Redstart after all; found a couple of pics of them with various small white patches; the song didn’t really fit though.  No, I didn’t have the app, but I walk the route a couple of times a week so I‘ll get it and see if lt‘s still there. 

No, definitely not, but thanks!

The photo has a very artistic look of being like a painting or print.