If yo ucan, I would highly recommend paying all or some of it on a CREDIT card - if your limit is not high enough, pay the cash into your credit card over the counter.
That way you are covered by section 75 (i think) consumer credit act 1974, where the credit card company is jointly liable with the dealer if anything were to go wrong.
If the dealer (like a lot of car dealrs) close down / cease trading etc, if there are any issues with your car, the credit card company would be laible to repair them