The B was an epochal car for MG. During its 18-year production run, it became the world’s best-selling sports car, and went on to define the concept of the open-topped British sports car for enthusiasts across the world. And since it went out of production in 1980 (by which time, it was already a classic), an entire support industry has grown up around it. When launched in 1962, a upto-the-minute specification meant it was a delight to drive compared with its rivals, as well as being a signifi…