Conservative feature as the alveolar tap and trill [ɾ r] were original to Old English but gradually merged with the retroflex approximant [ɹ] (think of that heavy r-sound in most American accents) in southern dialects during the Middle English period.

What do you mean by roll R's?

I am Scottish, can't say I've ever noticed it but living with the accent I guess I maybe don't hear it.