OK, I've been back and taken some more photos and put them in an album:
Birding UK and Ireland Forum - simon624's Album: Duck
I only think that this is probably the same bird. If it is then it seems to have picked up an injury to the top of it's beak during the week. As you can see from the comparison shots it does appear to be about the same size as the Tufted Ducks.
Simon.