Thank you Martin and Helder for your replies. There's definitely a lot
of information in those e-mails; I think it'll take me a while to read
through it all! I've done some testing and it seems the Martin's idea
of using the 'viewBox' attribute in the SVG file itself is the most
promising (and by far the simplest to do). As I have direct access to
the SVG file in question, I'll stick with this for the moment.
For anyone else that's stuck with this, I found a very useful resource
(in addition to the links Helder provided) that helps explain those
W3C recommendations .