Can't help you Malcolm but I can at least bump up your thread.
These are always tricky for non experts like me especially when it's not a great view.
I think on balance I would tend to go for Chiffchaff because of the prominent eye ring, dark legs, hardly visible eye stripe and dipped tail which is a feature of Chiffs.
However, I'm never confident with IDing these warblers so best wait for other opinions.
You don't have other views of it I suppose?
Unfortunately no, it was a chance photo. I've always been used to Chiffchaffs being more greeny-brown, which is why the grey back surprised me somewhat & the lemon breast. But it has the diagnostic eye-ring & lack of supercilium, I wondered if it was another subspecies.
First impression for me was possibly a young Garden Warbler. As Tony says though, they're alway tricky for non experts like myself.
That's a pretty good shout, Paul. It would certainly account for the greyish looking back.
I've uploaded a sharpened up image allowing the colours to come through better. The grey head and visible parts of the mantle are clearer as is the more extensive lemon on the throat, breast. Hope this helps.
Is the current photo in this thread the sharpened up version? Not convinced it's a garden warbler.