To make sure you purchase the right amount of cover for your vehicle, you should use the confirmed purchase price that will be listed on your invoice of sale. This should include any dealer options.
The following should all be excluded;
Deposit allowances, rebates, discounts, concessions, incentives, cashback, contributions, new vehicle registration fees, number plates, warranty costs, road fund licence fee, insurance premiums, fuel, areas, any negative equity and any other extras.
If you are leasing your vehicle, you should use the P11D value.