According to the The Oxford Guide to Style British usage of single vs double inverted commas differs from the US one:
Quotation marks, also called 'inverted commas', are of two types: single and double. British practice is normally to enclose quoted matter between single quotation marks, and to use double quotation marks for a quotation within a quotation:
- 'Have you any idea', he said, 'what "dillygrout" is?'
This is the preferred OUP practice for academic books. The order is often reversed in newspapers, and uniformly in US practice:
- "Have you any idea," he said, "what 'dillygrout' is?"
If another quotation is nested within the second quotation, revert to the original mark, either single-double-single or double-single-double. When reproducing matter that has been previously set using forms of punctuation differing from house style, editors may in normal writing silently impose changes drawn from a small class of typographical conventions, such as replacing double quotation marks with single ones, standardizing foreign or antiquated constructions, and adjusting final punctuation order.
Do not, however, standardize spelling or other forms of punctuation, nor impose any silent changes in scholarly works concerned with recreating text precisely, such as facsimiles, bibliographic studies, or edited collections of writing or correspondence.