Interestingly, a possible cinereocapilla (Ashy Headed) yellow wag was seen at Otterhampton Marsh on Steart today (ref @WWTSteart on Twitter).

There is a male Channel Wagtail in rough grazing next to Pitt Bridge on West Moor, Hambridge. 

See: https://twitter.com/alicksimmons/status/865579202292191232.

I initially thought it was a Blue-headed Wagtail but the powder-blue head, the large white supercilium and extensive white on the throat makes it more likely to be the former.  The photo on Twitter is poor but I have recorded this hybrid on West Moor before, in 2010, when I took better photos: https://goo.gl/photos/WLWf6ysvYZ97r6JH7  These show the white in the throat more clearly.

More information on this complex group and on Channel Wagtail can be seen here:  https://www.birdguides.com/webzine/article.asp?a=2058