once the lender has sold the vehicle probably at auction you will be advised of how much you owe. This will be the sum of your repayments including interest less the auction figure realised.
Whatever that figure will be it can be included in bankruptcy.
Just make sure that the HP details are entered in section 4 (secured) on the SoA and the potential shortfall is entered in section 4 (Unsecured). As you will not know the exact amount of the shortfall just enter £1 in the amount, a ? (or "unknown") in the date column, and "potential shortfall" in the reason for debt column.