The first two pics are the bird that looks more like (Greater) Scaup and without a close look to see the smooth grey back and the subtle peak on the crown, rather than larger rounded head this would be readily noted as Scaup. It can also show a hint of green sheen in the right light.The third pic is the other bird which is more easily noted as a hybrid with a reasonable view.
Bird 1 - seen from distance against the reeds in Marston Corner, Stewartby Lake from the old gull watchpoint. Looks like (Greater) Scaup. This bird has been noted on The Pillinge and Rookery North pits as well at least.
Bird 1 - seen from much closer notes the smooth back and bill with apparently no dark nail on the bill.
Bird 2 - Looks more like Lesser Scaup but again has smooth grey back which does not appear slightly lighter towards the fron like on Bird 1. The head shape has a much more defined peak and the bill clearly shows a distinct black nail with a lighter ring towards the tip.
Please take great care when looking at any potential male Scaup in the county.
Bird 2 seems to fit the style of described hybrids between male Tufted and female Pochard whereas Bird 1 perhaps is more of a mix of Tufted and (Greater) Scaup ?
We would welcome any comments about these birds please