Thanks.
I think your solution of using double quotes for outer quotes in the org document and having it changed on export is the way to go. The markup should be consistent and I see how having fewer single quotes helps things work properly.
However this is, at present, completely undocumented. This should be added to the manual. It took a trawl of this list to work out what was going on when I was using 'quotes' like this which is completely natural to us British.
Also, I vote for a setting. It seems that en-gb does nothing at the moment (I'm on the latest stable 8.3.2).
Anyway, no big problem. I now know how to write my org source and can look forward to a solution or work out my own. Just wanted to provide some feedback.
Thanks for all you do.