Dunnocks too were most active at this location on the 14th and are probably nesting nearby
Chiffchaff are busy staking their territory with distinctive calls at the edge of Centenary Wood, often making excursion to the hinterland as they forage for early grubs and other morsels. This image depicts a light phase generally found in southern breeds and in my experience resident warblers are not quite as yellow overall. There is variation of course.
This is the best time to locate Chiffchaff as they call from prominent positions blah blah - you can find all this in a book.