Can anyone identify this duck?

Seen at Widewater lagoon nature reserve, Shoreham Beach yesterday; what is it?  I can find nothing like it in my bird books.  Might it be a hybrid with some Egyptian goose in there somewhere?  I have no idea.  What do you think?

The RSPB people at Pulborough Brooks, had a look  on 22nd January and say that it is a hybrid Mallard.