Purple wildfowl

I went out for a cold and soggy walk at lunchtime round the lake. Lots of birds about but didn't spot the heron this time. I did see a pheasant and lots of moorhens poking around the edge of the lake. 

These ducks were looking magnificent in the sunshine. They had a fantastic purple metallic sheen on their wings and green necks. I've not been able to work out what they are so any ID would be appreciated.