The use of quotation marks, also called inverted commas, is very slightly complicated by the fact that there are two types: single quotes (` ') and double quotes (" "). As a general rule, British usage has in the past usually preferred single quotes for ordinary use, but double quotes are now increasingly common; American usage has always preferred double quotes.
British English often uses single quotation marks to identify the outermost text of a primary quotation versus double quotation marks for inner, nested quotations.
From wiki
Huh, just shows you how I was taught the British way many years ago, but adopted the American way due to reading so many bloody books!
Pull out your closest volume of Lord of the Rings and take a look. My copy at least has single-quotes for the speech text and double-quotes are used for nested speech. I guess it might be up to the publisher (eg: my copy of Harry Potter has been "Americanized" and thus uses double-quotes for the first level of speech text), but every copy of LotR i've run across uses single-quotes.