Great Northern Diver

.... I think? Although it looks different to the birds I've identified previously as a Great Northern Diver, maybe it's a female or a juvenile? I photographed two new birds for me today, a Goldcrest but it was flitting around a big tree so quickly that the shots were blurred, then a Grey Wagtail, which came out quite well but I hope too improve on it. It's good to have a bit of a challenge for my lunch time blipping!