This site is built using Jekyll and designed to be hosted using Github Pages.
To build locally (eg to test changes) you can simply clone the repository and then run
jekyll serve
and browse to http://127.0.0.1:4000
Content is mostly stored in normal HTML files. The key other files to know about are: _layouts/default.html for most pages and _layouts/home.html for the index page. Other useful config (when it is not stored in the Jekyll-standard YAML prefix on the HTML file) lives in _config.yml.
Contact Andy.