Eleven subspecies of the White Wagtail (Motacilla alba) are currently recognised and they all have slightly different plumages.
This is Motacilla alba alba, the nominate subspecies of the White Wagtail which occurs on the European continent and migrates down as far as Kenya.
Motacilla alba yarrellii (in Dutch: Rouwkwikstaart) is a subspecies that occurs in Britain.
It has a much blacker back than the nominate race and the black of throat continues on the side of the neck.

1st photo: Ezumakeeg, Lauwersmeer National Park, The Netherlands, 16 April 2021
2nd & 3rd photo: Naardermeer, Naarden, The Netherlands, 2 May 2015
4th & 5th photo: A juvenile. Oostvaardersplassen, Almere, The Netherlands, 26 August 2022