It's colouring is blue-grey, with pretty duck egg/grey beak.
Thanks for the help.
The neck is very definite, which led me to the possibility of wigeon, possibly juvenile going into adult plumage, but the beak makes me think not, no dark tip to it.....
I did wonder if it was a hybrid, wigeon/mallard cross.
I did say earlier, the beak suggested mallard to me, because it was quite pale and no dark tip which wigeon has. The neck line shouts to me wigeon, but I'm sure someone will have a more definite answer.