Confidence: It's likely to be this, but I can't be certain.
Notes: This bird was massive and unfortunately you cannot gauge scale in the image very easily. It was easily twice the size of a crow and in flight approached the size of a Buzzard. ID features - Flat head, huge hooked bill, shaggy neck, long rounded profile tail and long pointed wings that are nearly as long as the tail. Ravens have been recorded in the area.