Jaguar x type diesel 2004, glow plug light?

I have just bought a Jaguar x type diesel.It starts o/k but there is no sign of a glow plug heater light on start up.Does this mean the heaters are not working,or could it just be a failure of the light.I have only had the car a few days and not had time to investigate yet.I would appreciate some pointers before i start looking.