Section 75 of the Consumer Credit Act is the main protection you get when you Finance a car. It means you can hold the Finance company's toes to the fire if there is a problem. Unless you have a need to have a new car every 2-3 years or can put it through the books of a company you are always better off buying cash. Auctions are still a great place to get ex-fleet cars at 10-20% less than a dealer. You can buy a warranty if you need.
One of my cars I've owned for 17 years from new, another is 9 years old, they were reasonably expensive (30-40k when purchased). I reckon I've lost about 2k a year. Had I purchased a new car on Finance over 3 or 4 years - I'd be losing 5-10k per year. With older cars, you can also save on dealer servicing, which adds up over time.