I am glad that others fly in the face of publishing convention!
Investigation time! I just looked at some novels published by Penguin, Bloomsbury, Vintage, Jonathan Cape, Picador, Headline, Oxford University Press and ATOM. The ATOM book was the only one that used double quotation marks (and it used them for both speech and setting-aside), but that's probably because the book in question was (ahem) New Moon and therefore originally American. I don't have any ATOM books by British authors, so I don't know how they compare. (The Picador book was also American; presumably Picador's style guide recommends single quotes no matter what a book's origin.)
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Investigation time! I just looked at some novels published by Penguin, Bloomsbury, Vintage, Jonathan Cape, Picador, Headline, Oxford University Press and ATOM. The ATOM book was the only one that used double quotation marks (and it used them for both speech and setting-aside), but that's probably because the book in question was (ahem) New Moon and therefore originally American. I don't have any ATOM books by British authors, so I don't know how they compare. (The Picador book was also American; presumably Picador's style guide recommends single quotes no matter what a book's origin.)