http://en.wikipedia.org/wiki/Fellowship_of_the_Royal_College_of_Surgeons

Holders of FRCS (and the new, but not old, Membership – MRCS) often choose to relinquish their title of “Doctor”, reverting to “Mr”, “Mrs” or “Miss”. This is a relic from times past when surgeons did not attend medical school and were simply skilled tradesmen, amputating limbs or removing bladder stones, and learning their skills through apprenticeship.

-Brett