I thought I had found a female American Wigeon this morning – I knew there were two types of female Eurasian Wigeon – rufous and grey – but it wasn’t until I got home that I found (courtesy of Steve Madge) that there was an intermediate between the two – now I am not so sure.
Glamorgan Bird Club 
Lol, looks like Eurasian to me, but as I’m sure you know the underwing is what you need to see well
As you say Barry – the white auxiliaries are the key separation feature – and getting them to fly is tricky 😉