David has answered Cliff's alba wagtail query.
Just to confirm my approach to recording these. When I'm uncertain of the identity of the subspecies concerned - Pied Motacilla alba yarrellii or the White nominate M. alba alba - I record them as “alba” wags. Unfortunately, due to distance and light, it was not possible to confirm all seen at Angle on Sunday in a small flock to subspecies level.
I don't know if we see "hybrids" in Pembs., but I do recall in May at Stackpole (a few years ago) watching a very smart male M. a. alba attempting to mate with a female M.a. yarrellii. A male of the UK subspecies was having quite a hard time driving it off! Mixed pairs have been recorded previously in Scotland, in the Northern Isles and the Hebrides (Birds in Scotland 1986).
Bob