A tufted duck maybe?..

Hi there

Saw this lone bird on a remote highland loch yesterday. Apologies, I was quite a way from it and in the car so have had to give the photos quite a crop. Though it was a grebe of some sort at first until I looked at photos today and eye colour all wrong for a start. It's probably a tufted duck or some such but it didn't match winter or summer plumage as shown in my RSPB book so can anyone help please?