The website is built at present using an ant-based build process in
which chunks of content are topped and tailed by the build process to
produce full HTML pages.

Thanks -- I've made my initial changes using the ant script and as you've described.  In fact, I've got a few updates for the ant script that I'll check in soon.  The mock-up is at an early stage -- when I get it just slightly better I'll be ready to put it wherever we want -- I'll have something to show by sometime this weekend.