Ok so the answer, courtesy of herrstrietzel was to add the viewbox information to the inserted code, this allowed the SVG to scale with the div properly, as (he said) the viewbox information in not copied from the svg definition.

I also had an additional issue that was resolved by adding display: block; to my CSS for the SVG, this removed the additional height added around the SVG and removed the remaining display issues. (this was also the issue when hardcoding the width and height).