What do you think ?
So some homework was required.
It was the second image and assistance from the ID section of Birdforum ( with thanks to Stevethehydra - Full name not known ) that finally clinched it.
The conclusion is that it is certainly a duck and close to ( if not a pure example ) of the Aylesbury breed - a "heavy" duck which is a lot larger than the wild-type Mallards that it was ultimately selectively bred from.
People are often surprised by the size of "heavy" domestic ducks!