It's important to understand the different types of finance.
Most of the finance deals bring referred to above are not in fact leasing, but PCP deals.
With a PCP (Personal Contract Purchase) you buy the car. You pay a small deposit and finance the rest. An APR on the financed amount will be charged as you pay interest on the amount financed. You pay a monthly repayment and at the end of the term, typically 3 years, you either pay off the remaining finance (or balloon payment) and keep the car, hand it back and walk away, or use any 'equity' in the car as your deposit for your next PCP deal on a new car. Your balloon payment is the same as the minimum value the dealership set at outset as the amount they think your car will be worth at the end of the term, assuming a certain mileage (say 10,000 a year). They tend to be fairly pessimistic about future values in truth, to protect themselves. If you hand it back and you're over the mileage you'd pay a few pence per mile penalty as obviously the car will be worth a bit less to the dealership if it has more miles on it.
With a lease you don't buy the car. It remains the property of the leasing company. You pay an initial rental payment (a bit like a deposit) followed by a monthly rental payment based on agreed mileage, often 10,000 a year but this can be changed.The initial payment and rentals are subject to VAT. Most deals are over 3 years. At the end of the deal you hand the car back, end of story. Again, small charges apply if you go over the mileage allowance. You then lease another car if you want to, from whomsoever you choose.
I've done both. Which is better? It depends on the car, the mileage etc. But as someone said, it also depends on which manufacturer is keen to shift cars. If you're flexible on car choice, so much the better.
My personal preference is leasing as there is less 'smoke and mirrors' - what you see is what you get. You're effectively just paying for depreciation without the hassle of renegotiating with a car salesman every three years who'll be trying to give you no discount on your next car and a rubbish trade in for your old one. "Sorry, there's very little equity in your car, etc..."
I loved leasing as all the deals are out there on the web. it was done within the comfort of my home with computer and a phone. No garage visits, no salespeople, no haggling.