Of the 10 Chiffs, most were rather normal-looking, but one bird did look rather eastern... It's possible this is just a rather bright tristis Siberian Chiffchaff and it certainly called like one when released. But it does have quite a lot of green tones on the mantle and flight feathers, so not the most straightforward.
In comparison, all of the other birds looked more like the one below which was interestingly already ringed. We won't get the details on this bird for a while, but the ring was issued to East Dales Ringing Group in North Yorkshire, so a nice green collybita it is. Supposedly a photograph never lies, but check the difference in plumage tones in these two pics of the same bird: top a fancy DSLR and bottom my iPhone. Not surprisingly the DSLR looks to be a truer reflection of what the bird should look like!