It looks much more like a gull than grebe/diver to me. Possibly Common Gull (Larus canus). Take a look at the skull site , they have this photo and others. (Your skull doesn't have the rhamphotheca - the horny sheath on that covers the bill, so you have to consider this when comparing). On a Wild about Britain forum there is this image that could help you diagnose your specimen.
Thanks for sharing this.