I saw a warbler today on the Queens Road allotments in Leicester. But which, I haven't a clue. I got a really good view and I would say it tended towards buff underneath rather than yellow; brownish above rather than greenish and the eye stripe wasn't very prominent with the dark stripe more noticeable. It refused to sing. Its feeding habit was very characteristic, moving along a boundary of brambles very acrobatically in short flights. In a case like this, is it possible to enter a generic spot like "warbler" rather than plump for a definite ID?
The most common warbler at the moment seems to be the Chiffchaff and I suspect from your description this is what you saw. We don't have a generic 'warbler' entry I'm afraid, but if/when you hear it sing you may be able to confirm the species.