but what drinks are non-U and beyond the pale?
It's easier to list the more acceptable drinks - by all means ask for a Red Wine, White Wine, G&T, Scotch (with water or ice only), or just water and you will be relatively bomb proof. Don't ever start being a wine snob ("cheeky little bouquet with a hint of tarmac") or you might as well replace the "s" in "snob" with a "k", and definitely stay off the exotic liquors. Getting into a boat race with Green Chatreuse is not the stuff careers are made of - unless you win of course.
Beer may be offered, but then you run the risk of demonstrating your girly bladder control, while those with bladders like a space hopper are able to maintain a semblance of continuity to their social intercourse. This advice is only pertinent if you intend being invited a second time, otherwise asking for a pint of Creme de Menthe and pork scratchings is the only way to go, making sure your RAFA badge is prominent on your track-suit top.