and to Dave Britton for the following comment.
BirdNet are reporting a hybrid Glaucous/Herring Gull at Shirecliffe Tip (near Sheffield) this morning (19.02.14). They wrongly call it a Nelson's Gull (that term is usually reserved for hybrids of Glaucous and American Herring Gull). I've let them know this error. This might be a different bird of course but interesting as the adult Kumlien's Gull has wandered between these sites.
Link to video clip: http://www.youtube.com/watch?