Do you have to inform insurance of a Res delete?
Yes, IMHO you would need to inform them.
If you check the small print of your insurance policy, there’ll most likely be a clause that requires you to tell them of
any modifications. Some will go on expand to on this and provide their definition of a modification (what is considered a modification can vary from one insurance company to another), which is usually anything that changes the factory spec of a car when it was originally built. Having said that, I don’t think an insurance company needs to know if you’ve made a ‘modification’ such as fitting a set of mud flaps - which strictly speaking has changed the factory spec of the car!

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Modifications can be a bit of a grey area and I’d say if in doubt, then always declare it as not doing so can be considered as insurance fraud - i .e. dishonestly obtaining insurance without declaring all the risk information for the insurance company to adequately assess the risk and charge their ‘correct’ premium. Insurance fraud is a criminal offence which if convicted, would need to be declared on future insurance applications and could affect a person’s ability to get insurance cover in future at an affordable price.