Could it be Wood?

Unfortunately not. A large looking Phylosc was lumbering through a Downy Birch Betula pubescens at the back of our garden today and when watched through the bins, showed a fair amount of bright yellow. Adding to the suspense a little by not singing or calling, I decided to scope it. I don't mind admitting being a little rusty on key features, so having read up a little I found the following. The yellow should appear brighter for Wood Warbler and more restricted to the throat, ear-coverts and breast sides. The underparts on Wood Warbler are a much cleaner white, with a cleaner transition between the yellow(around the throat) and white underparts. For silhouette birds, a nice feature to look for in Wood Warbler are short tail and very long primary projection. This bird displays none of these features and is of course a Willow Warbler.