Hi Jester as far as I know it usually on the bottom of the fuel injection pump - on some models it can only be removed by taking the pump off the engine. Try contacting a diesel specialist and they may be able to advise. Their is also a solenoid on top of th epump which is the stop solenoid. As a matter of interest what is the problem with the car.
I'd check to see if there is a Lucas Diesel Service Centre near you.My local one in Yeovil (Somerset) is excellent.They are very helpful,very knowledgeable and the quality of their work is second to none.