that is seriously bad, glad you weren't hurt mate.
I dont think anyone would risk going back for the code to a car that had an anti hijack device if they had already driven away they would know you had called the police as soon as they left.
I think I might also re-look at the Tdi badge, although I dont think they made noggy blue avants in Tdi
I was halfway through a project of making my own tracker a few years ago, its pretty simple as you can buy GPS 'chips' relatively cheaply, and you can use a pay as you go phone simcard to activate it (ie call up the buried sim in the car and it starts the GPS running and transmitting current position via GSM), and then you can use AA roadmap or equivilent to track the car. its cheap and can be hidden relatively easily, no monthly costs. I think it would relatively easy to rig the system up to activate a relay and stop the engine, or for s4tan.... rig it to lock the doors, and spray pepper spray through the vents! ha