Sea Bird ID Please

We saw the bird below swimming and diving in the main channel in Wells Next The Sea on N Norfolk coast on Thurs lunchtime as the tide was going out. It was some distance  and at first thought it was a Little Gebe but I thinks its body is too long and its beak a bit long and colouring wrong for a grebe. Could it be a juvenile smew or something else?

Any thoughts/suggestions would be great.

Many thanks.