Hi everyone - thanks verymuch for your kind replies.
The only thing- it was 100% not a Coot - unless it was Coot like no other. I'm from East Anglia and Coots are abundant in 'these here parts', I am very familiar with Coots (some more than others - a baby Coot tried to peck my finger once)! What I saw was bigger than a Coot, although I can see why people thought it might be a Coot. It was fatter than a Coot (for want of better words to describe it)!