Mad Mac - for once we will have to disagree on a financing question but I specialised in this kind of lending for over 6 years and can CATEGORICALLY state that a personal loan puts no link between the provision of finance and the asset.

If the OP really has signed a Personal Loan Agreement he is free to sell the car at any time, but is obliged to continue the repayments until it is repaid in full, and he has no right to return the asset and walk away under HPs half/third rule. (He needs to check the original document because the finance type on HPI could simply be an input clerk entering the wrong code).

As posted by FocusV8 above, the finance is disclosed on HPI to make other potential lenders aware that the OP has this outstanding debt, and help minimise the risk that he ends up with multiple loans for cars that are sold on and turned to cash with no means of then servicing the debts, or assets that can be repossessed, but there is no reason why a potential purchaser should be put off by this as they will have clear title to the asset.