Don't be dissapointed Adrian. The bird in your picture is obviously quite unusual and is not pictured from a typical angle.
I'd hazard a guess at a Blackbird judging from it's low hanging wings, tail shape and it's longish yellow beak. Seen on a garden fence also backs up the theory. The white discolouration (strange looking as it is) is something that happens from time to time and nothing to do with winter plumage. Just one of natures oddities.
Hope this helps answer your question.