This is still WIP but does work.
Download the zip file and extract the "Britannia" folder into the "$FG_ROOT/AI/Aircraft" folder.
To use you will need to create a traffic file, see the wiki for instructions. http://wiki.flightgear.org/AI_Traffic
A simple AI Traffic Creator (Python and a 64 bit windows) is available here: https://github.com/gooneybird47/FlightGear-AI-Traffic-Creator
I have included a few traffic files that are based on the actual routes flown but the times are not accurate. To use drop the "brit-traffic" folder into the "data\AI\Traffic" folder.