The general rule in British English for stacking honorifics is that you add
one honorific of each type. "Professor" and "Doctor (Dr.)" are both academic honorifics; only use one of them. If, on the other hand, you happen to be a priest with a knighthood and a doctorate, you sit in the Commons and have been awarded a CBE... "Rev. Professor Sir John Connor, M.P., CBE" —
ArtOfCode Jun 9 at 11:54