I've got myself into a right mugger's buddle with these quotations and dates, what with reading both in the wrong sequence! In fact, the first time the phrase - in the form "I signified my contempt of him by thrusting my tongue in my cheek" - appeared in English print was in 1748 in Smollett's 'Roderick Random'. The Scott quote was much later and the 1748 date is clearly the one referred to in E's opening response above. In the form "tongue in cheek" - just these words in that sequence - it did not appear until the 1930s and the hyphenated form "tongue-in-cheek" was even later, in the 1950s. Sorry about the confusion, Cueball.