Pied wagtail
The car park wagtails are a pair of grey wagtails but we have pied wagtails too.
Pied wagtails are common and familiar, seen in towns and cities as well as nature reserves. They are easily identifiable by their bold black and white markings as they dash about wagging their long tails up and down,
1 
2
[1] Grey wagtail (Motacilla cinerea) [2] Pied wagtail (Motacilla alba)
Pied wagtails are insectivores, but will feed on seeds and bird-table scraps in winter. Most are resident here but in the winter, those that occupy northern upland areas will move south to escape the cold. Sometimes they travel a lot further south than Wiltshire: they have been spotted overwintering in North Africa. As the temperature falls here, the residents will flock together at warm roost sites like reedbeds, trees and bushes.
In summer, pied wagtails nest in ivy, under roofs, in walls, between stones, in all kinds of hidden places. They defend their territories fiercely, usually raising two broods of five or six chicks every year. Their numbers are stable and there are believed to be almost half a million breeding pairs in the UK.
Keep an eye out for them and send us photographs if you are lucky enough to spot them.
Southwick Country Park Nature Reserve 
We used to have a ‘white’ wagtail that came every winter, from the first frost. He only ate crumbled digestive biscuit.
Sadly he didn’t come last year!
I think pied wagtails and white wagtails are the same thing, though not everybody on the internet agrees. The RSPB and Wikipedia give them the same scientific name: Motacilla alba.