Various, Notes and Queries, Vol. IV, Number 97…
“ The Lord Mayor is certainly not a privy councillor by reason of his courtesy style of Lord, any more than the Lord Mayor of York.The question is, whether the style of Right Honorable was given to the Lord Mayor from the supposition that he was a privy councillor, or from the fact that formerly the Lord Mayor was considered as holding the rank of a Baron; for if he died during his mayoralty, he was buried with the rank, state, and degree of Baron.When does it appear that the style of Right Honorable was first given to the Lord Mayor of London? ”
