I don't have a quote to give you, but I can give you some context. I was recently rereading Agatha Christie's Death on the Nile. I've read it before but not for a long time, and I noticed something that I never have before, and that's that one of the characters uses the terms lemonade and lemon squash as though they were synonymous. By that I mean that she refers to a specific drink first as "lemon squash" and then just a sentence or so later as "lemonade." I was under the impression, though goodness knows where I got it, that these drinks weren't exactly the same. Was I wrong about that? Or did Mrs. Otterborne make a mistake? (She did like her liquor, after all.) Or do some people use them synonymously and others do not? I should add that I've never heard of lemon squash in AmE. It seems to be either a British thing or a BE term.