Back on the 1st February I mentioned in the caption under my Drozmary scaup video that I wasn't completely convinced on the ID. Since I've come back home I've had more time to look back at the videos that I took and am now content that it's a lesser scaup. Below are some grabs showing the salient features. When I saw the bird it was diving in the company of a female tufted duck and I can confirm that the scaup was of comparable size to the tufty.
Here is a compilation video of all the footage that I took of the bird.
I also asked my "go to" ID guru, the long sufferring Ian Lewington who patiently puts up with a lot of my often ignorant ID queries, what he thought and he couldn't see any problem with it being a lesser scaup. He said that it definitely wasn't a greater scaup but he couldn't tell from the video whether it might be a hybrid. I guess that a decent open wing view will clinch it for definite but for now it's going down on my year list.