How "policeman", "constable", "bobby" and "cop" differ in the sense of connotation?

How "policeman", "constable", "bobby" and "cop" differ in the sense of connotation?

AMONG THEM, "POLICEMAN" AND "CONSTABLE" ARE STYLISTICALLY NEUTRAL, YET THE FORMER IS USED BOTH IN BRITISH ENGLISH AND AMERICAN ENGLISH WHILE THE LATTER IS ONLY IN BRITISH. "BOBBY" IS COLLOQUIAL, USED ONLY IN BRITISH ENGLISH AND "COP" IS SLANGY.