Historical note:

both porter and stout developed in London in the late 18th century. The characteristic creamy head was originally achieved by having two (or even three) barrels of naturally conditioned stout (fermenting in the barrel) available: a mature barrel (or two) low in CO2, that provided the body, and a fresh, rapidly fermenting barrel to give the head.

Paddy's day in England used to drive my mother mad, because we all had to wear sprigs of shamrock, and she didn't want to be taken for Irish- her mother was from old Lancashire Recusant stock!