advice needed

[j4gz]

if you change your suspension on your vehicle do you have to notify your insurer ie have coilovers or lowering springs

[Speedtouch]

You should, in theory, declare all modifications.

However, if the springs are only slightly lower (e.g., M-Tech -15mm), then there's probably no need.

[Brianmoooore]

As a general rule, you can probably get away with not declaring anything that was available as an option on the original car, or close aftermarket equivalents of those options. When it comes to things that detract from the safety and road holding of the car, such as cheap coil overs or excessive lowering, then it needs to be declared. Anything that makes the car more attractive to a thief needs to be declared as well.
Don't forget, the insurance companies make the rules, and you agree to abide by those rules. They'll happily take your money right up to the point when you, or a third party, tries to claim some of that money back in the form of a claim, but if they then discover that you haven't followed the letter of those rules, they are completely within their rights to void your policy and leave you to pay the claim yourself, possibly in instalments for the rest of your life.

[Captain_Birdseye]

If you have breakdown cover bolted on to your insurance then it's probably going to be your insurer who pass on the details of what kind of vehicle you have to the breakdown co.

If you have a car which is too low to use the standard equipment on then you might need the special lorry to recover your vehicle (they say coke can height off the ground at front of car for one test of height for example). I'd bear that in mind when making your decision as you and the breakdown will both be happier if they send the correct recovery vehicle.

It might vary from company to company, I’m only speaking from experience as I had a lowered car and I was glad I’d declared it for this reason.