New duck in town

[Thunderbird+]

Among the many mallard ducks in a local park lake, I've noticed a new-commer has turned up within the last couple of days and I wonder if anyone can identify it for me ?
Its basic colouring of its back and wings is similar to that of a female mallard but the head is differant. It has a chestnut brown marking that go's over the top of the head, leaving the rest of its face white, its bill is grey/brown but orange near the head.
When it stretched it wings I noticed two jade green markings on each.
I cant find anything in books like it. Any ideas ? thanks

[Cetti]

Is there a chance it could be a hybrid Thunderbird, as Mallards are notoriously promiscuous and will mate with just about anything?

If it looks like a species in its own right have a look at these females: Eider and Scaup. Not much help am I?

[Cetti]

Forgot to mention that Mallard males are going through their eclipse stage up until September, so will look very like odd females.