Thanks, all - some very interesting responses.

fwiw, I too have heard and used both variants - interesting thought, plute, that it could be a question of which attribute is thought to carry most hono(u)r. I think, too, that there was a definite English class-system loading in the phrase: someone was either a gentleman or a member of the ghastly hoi polloi... ;) And that was true of students at Oxford and Cambridge too.

Yep, the Rabbie quote was the one that prompted my original turning to sources, and given that I had believed it to have earlier antecedents I was surprised by the paucity of information I could find. Yes, I'll try W/O Fong - is it Dr Techie who has access to a corporal data search tool for millions of US literary sources?

I think the consensus view emerging ~ that the phrase or a variant is typically used as a genuine compliment, with a self-deprecating edge of twinkling irony inherent in the over-mannered construction ~ represents all the typical occasions I have heard it used.