If I have a Comprehensive insurance policy, what happens (in the event of a total loss) if the loan on my vehicle is more than the market value determined by you?

This scenario can, and does, happen. We are only required to pay you the market value of the vehicle or the sum insured as shown in the policy schedule, whichever is the less, at the time of loss and not the loan balance payable to your lender. Your lender will look to you to pay the shortfall to them in such scenario.