What is the name of the British comedy movie made early 1970s (or late 1960s)? Set in the country home of a middle aged couple, its Christmas holidays, snowing outside, the heating in the house can't be controlled or turned off, so it's like a sauna inside. Son comes home from college for the holidays with "friend" who is of indeterminate gender, father spends the next couple of days trying to establish gender of "friend" - like seeing if toilet seat is left up when used, and so on.

Thanks, Leo.

My British sources suggest that it is Girl Stroke Boy (http://www.imdb.com/title/tt0067137/).