Marsh Warbler is also a schedule 1 bird, so if there really is a nest, I wouldn't advertise it. Except with superb views, it can only be separated from reed warbler by song. Given the abundance of reed warblers at Ham Wall, that is the far more likely option - but still a very nice set of photos.
Yes. They look identical to me. Although the couple who showed it to me did say that they identified it by it's call. Still I was happy with whatever it was!
