Another Pied Wagtail

This bird looks different from the one I posted the other day. I think there are different  forms or subspecies of Pied or White Wagtails which may be visiting us this winter from the continent. There are at least three individual birds visiting my Mum's garden  at present, and each one has different plumage, this one being the darkest. I find it very interesting and curious, and I need to do more research, although that risks me getting even more confused!  Still, lockdown provides a golden  opportunity  to  study the garden birds more closely than usual.