Assuming the car was bought on Hire purchase regulated by the consumer credit act the legal position is that the hirer (finance company) owns the car until the end of the agreement, you have the right to terminate the agreement provided the hirer has not done so and return the vehicle, if more than half has been paid you will owe nothing except any arrears on payments due. If you default on payments, which it appears you have, the hirer can repossess the goods but will need a court order unless you agree or less than one third of the purchase price has been paid.
If the hirer repossesses the goods you will be liable for the total sum due under the agreement less the sale proceeds and payments made. The hirer can obtain a warrant of delivery, which will allow the county court bailiff to seize the car, I would suggest you try to negotiate with the hirer and offer payments, which will realistically repay the agreement and arrears or consider a time order which is made under the consumer credit act in court and payment by instalments too which the court has agreed.
Hirers often claim that the court can only make a time order in cases of temporary financial difficulties, but this is not correct.