http://www.ornitho.ch/index.php?m_id=54&mid=31964 (http://www.ornitho.ch/index.php?m_id=54&mid=31964)
I am not sure-What do you think this is? Photographed in Switzerland (not by me, just found the pictures).
(Common Pochard x Ferruginous Duck) x Common Pochard?
Or Common Pochard x Redhead (because of bill and iris colour)?
It is considered to be a Common Pochard x Tufted duck 2nd generation hybrid in that link;
I thought it could be a backcross (Common Pochard x Tufted duck) x Common Pochard ; or the possibility of redhead x pochard (Thinking along the same lines as you, Gert-Jan....)
But how to differentiate between these possibilities???