Much depends on the point at which we decide that RP came into existence. William Gladstone, who was PM for four different terms in the late 19th century, went to Eton College yet his pronunciation gave away that he was from the North of England and his speech was criticised by RP speakers in the early 20th century.
Definition of vane. 1a : a movable device attached to an elevated object (as a spire) for showing the direction of the windb : one that is changeable or inconstant.
Vain means self admiring or futile. (The term in vain means without success). A vane is a stabilizing fin or blade. The words vein, vain, and vane sound identical, but their meanings are very different. The noun vein has several meanings: A blood vessel that carries blood from the capillaries towards the heart.