Hybrid female would be my guess but not sure what other duck is implicated.
Leucistic female pintail??
TBH almost anything is possible with ducks!
Nice shots,Chris. My favourite s the Spotted Redshank,possibly as I haven't seen one yet. I'm a beggar for moderate,careful cropping but do you think a bit of cropping would enhance them especially that lovely shot of the kestrel..the redshank too.