Traditionally, parts of Lancashire have very clearly articulated "r"s, similar to the stereotype of Cornwall and the West Country. The pronunciation of these "r"s towards the ends of words is called rhoticity.
In fact, historically, hundreds of years ago, people throughout England used to pronounce strong "r"s. But now, says the research paper, these strong "r"s are definitely dying out.
In Blackburn, young speakers do mostly say their "r"s, but they are, according to the research team, phonetically very weak and often difficult to perceive. And they pronounce them less frequently than older speakers.
Not quite - though I’m not sure what you mean exactly. It’s about “ar” being pronounced either like “ah/uh” or “aRRR!/uRRR!” (Like a pirate, or breakfast cereal Tiger).
If “Baa” like a sheep and “Bar” like where you order drinks in a pub are pronounced the same, like “bah” = non-rhotic.
A pirate, or farmer from cornwall saying “Arr!” is very Rhotic.
As far as I’m aware, the majority of American accents are rhotic