Another Beds Great northern Diver

I was out today to do my WeBS count of Roxton. Roxton really has gone downhill in the last year and recent visits have been pretty birdless. Today started well with a female Red-crested Pochard - a site first for me and a year tick. I nipped back to the car to get my camera but couldn't relocate the bird. Thinking it may have flown to the oldest lake along the river (which is normally very quiet indeed), I decided to pay a rare visit to this lake. This is very rarely watched and I only visit about 4 or 5 times a year. True to form, the lake had 5 or so Tufted Ducks and a Mallard or two and the flock of Greylags. Then I saw what I assume would be a Cormorant but it looked a bit pale.... Raising my bins revealed a Great northern Diver. From photos of the other two, I'm sure this is the third found in a month. The Priory bird looks darker around the cheeks. I spent some time trying to photograph it but failed apart from the above.