White Wagtail, photographed in Herne Bay, Kent (17 April 2010)

Just found this photo of what I believe could be a White Wagtail, judging by its pale mantle and flanks as well as the sharp contrast between the nape (black) and the mantle (blue grey) it could be one.  I took the photograph on the 17 April 2010 on the coast near Hern Bay, any opinions on confirming the ID?

confirmed White Wagtail, seen 17th April 2010 at Herne Bay