You better call them ASAP because if you make any modifications without telling the insurance company crash, the loss adjuster will deem your insurance null and void and you will incurr the costs, god help you if its your fault.
A story from another forum, READ CAREFULLY
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If you put kit on a car and do not declare it, if you claim against the policy then if the loss adjuster turns up and says you did not declare that nice new grill thats not standard even though its made by Peugoet then forget even going any furthur. They are not stupid people.
In fact my mate was in the same spot, thought he could bluff them and the loss adjuster who came had a photo of an unmodded car as it left the production line.
Policy ----> Smoke
That left him a bill for the car, outstanding finance, a heafty fine for having now, in the eyes of the Law no insurance, penalty points and no car. (and damage to pay for to street furnature)
If you think its cheap to not bother telling them then run the risk, Id rather pay another £100 or so than get caught in that trap.
If you can afford the mods you need to put the insurance cost into it. If you run into me with a modded car and under insured then Ill gladly point it out to them, why do I have to pay full whack whilst you dont?
If the insurance company can find a way not to pay they will