Put the balance on a credit card, then swap to a card with an interest free period.
As an example, a balance of around £9k will have a minimum payment of around £200 per month. The cost to transfer is usually around £250 (3%) first time, and less second time. So you can get the car and only pay the transfer fee twice in your 3 year repayment period (many cards have over 18 month 0% windows). If you pay £264 per month, you will pay it off in the 3 years, including the balance transfer fees.
Doing this will greatly reduce your "interest" payments, as after, say, 22 months (Barclaycard have 22 month 0% on transfers), your transfer balance would be around £3432, so would only incur a fee of about £102 to transfer, and assuming you keep making payments of £264, you will have paid it off in full by month 36.
Doing this means an overall "interest" payment of around £352 over the 3 year term, which will be untouchable from banks / dealerships.