No sex please, we are British!
No Sex Please, We're British was a long running comedy in British theatre (1971 - 1983), written by Alistair Foot and Anthony Marriott. It was later made into a movie.
SUPPLEMENT:
There is a reference in a 1963 edition of Bookmarks, a literary periodical, reporting on the banning in Ireland of Helen Gurly Browm's book, Sex and the Single Girl. The headine read, No Sex, Please, in Ireland.
An ngram of No sex please does not seem to indicate any earlier references.