Why do some British (English) people add a pronoun to the end of a sentence?
It looks like right dislocation to me, just with utterances without an explicit subject. (It’s not always a pronoun and the concept itself isn’t specific to England.)
Here’s a paper with a similar example:
Situation: A has told B about how he slammed his finger in a car door.
B: Agonizing, that. Car doors are always a problem.