I think its an Upchers Warbler.
Its clearly a hippolais warbler for several reasons, including head and bill shape and a lack of a supercillium beyond the eye.
The wagging tail is a good field character of Upchers, and the apparent size and shape look good for that species as well. The tail looks contrastingly dark, although i accept that it is in shadow and therefore looks darker than it really is. The pale edges to the primaries and secondaries are a well known feature of Olive-tree Warbler, but are also present on many Upchers. Actually, the ID of these two species in autumn may be more tricky than first thought, after the confusing bird on Shetland last August.