Strange you say that much about the spoiler, when I asked my insurance about lowering my car less than 5cm they said this;
Which makes yours sound ridiculous!
There will be an additional premium of £30.16 from now till your renewaldate to note this modification. This would be spread over your monthlypayments. Please note our standard part's clause would apply. Please adviseus if you have your suspension lowered under 5cm.
Which makes yours sound ridiculous!