Unusual Small Brown Garden Bird with White Tail - What is it?

Please see attached images/video.

Small brown/rusty colour bird, around the size of a Robin or Sparrow. Top of tail completely white, extending up its back about half way.
Was seen ground feeding then flew up on fence post.
Sorry for the poor quality images, they were taken on a phone through an upstairs window in a hurry. 

Video on youtube:

https://www.youtube.com/watch?v=93817odWAb0