What devilish bit of British humour was I missing out on, had Pigou slighted Keynes in some talk and therefore the emphasis on his position as professor as Keynes disagree with him?
Well, a conversation with Vicky Chick suggested a more sedate explanation, one of British politeness rather than sardonic wit. In writing it was only proper to refer to ones contemporaries by their full title (mr, mrs, dr, prof etc) while those who had passed away would not have a title - something which also meant you could distinguish between who was being referred to.
Having trawled back through my GT and found a good ten professors with the full reference who were very much alive when the GT was published, and only name references to people who had passed away (Marx, Edgeworth etc) that seems to settle that. Keynes had some 10 full professors and a major from the Royal Airforce Engineering corps. This is of course a pre-cursor (of sorts) to our current referencing system, where we implicitly refer to other authors as dead. Nice.
Oh, the ten professors were: Professor Pigou (1877-1959), Professor Hayek (1899–1992), Professor Robbins (1898-1984), Professor Irving Fisher (1867–1947), Professor [Gustav] Cassel (1866–1945), Professor [Thomas Nixon] Carver, Professor [Frank William] Taussig (1859–1940), Professor von Mises (1881-1973), Professor Alvin Hansen (1887–1975), Professor [Eli] Heckscher (1879–1952) as well as Major [C.H.] Douglas (1879–1952).