Diver?

Hi, sorry for the terrible photos but they were the best I could get. This bird was out in the middle of a wide stretch of sea-river, so was pretty far away. Unfortunately I turned away for a few minutes before taking some more photos and the bird looked slightly different in these later photos (I don't know if it was the same bird from a different angle/lighting, or a different bird all-together, but given it was in the same place as the first one I am assuming it is the original bird). My best guess would be a diver of some sort, but I am also leaning towards a guillemot, as you don't normally find divers here.

And here is the bird (that could be the same individual) that I thought looked different.

Any help you can give is appreciated, thank you!