Having worked for an insurance company, I have voided policies that have had modifications on cars.
Inevitably, these modifications only came to light during a claim, so had it just been the policy holders car then we wouldn't pay out and simply give back the policy payments they have made minus any admin fees.
If it involves a third party, we would deal with the TP as RTA insurers (basic legal requirement) then look to recover costs from the policy holder.
It does go on. Insurance companies will do anything not to pay out and non disclosed modifications are the easiest.
Inevitably, these modifications only came to light during a claim, so had it just been the policy holders car then we wouldn't pay out and simply give back the policy payments they have made minus any admin fees.
If it involves a third party, we would deal with the TP as RTA insurers (basic legal requirement) then look to recover costs from the policy holder.
It does go on. Insurance companies will do anything not to pay out and non disclosed modifications are the easiest.