Be very careful! If the car has outstanding finance on it then it is the property of the Finance company and NOT the prospective seller.
"Before you buy a secondhand vehicle, it may be worth checking whether it is still on a hire purchase, conditional sale or leasing agreement. If it is, you may not have 'good title' to the vehicle (be the true owner). To find out whether the vehicle has any outstanding agreements on it, check in the telephone directory, or search the internet, for 'vehicle history checks'." (from CAB)