[chris_s1]

Its the same with aftermarket alarms as well. I once had a Clifford system fitted to a car that didn't have a Cat 1 alarm as standard. They put my premium up by about £40 IIRC (this was some time ago).

I believe the reason is - they may or may not give you a discount for extra security but they DO consider it a modification and load the premium accordingly.

So you might be getting 5% discount for having a tracker and 10% increase for declaring a modification. Depending on the insurer's view on mods vs security this will vary between insurers and indeed between cars with the same insurer.