doesn’t seem to have had any effect. We’re also using IIS so I added a script map handler mapping for .html but this has the effect of killing the site - just showing a blank page

Maybe post your web.xml file, as just cutting and pasting what Adobe has, will not work. You need a handler for CFC/C/M/ML files, and to be honest, this setup is painfully inefficient. as normal and then map .htm/html isapi extension to use CFM/L/C/ML executable. Right-click on "Web Sites" in the IIS Manger, sites list. Go to "Properties". Look at the ISAPI extensions. Find the htm and html extensions and change executable to the same as .CFM.