Not many years ago the very idea of a mainstream C-segment car with combined fuel economy in the mid-70s and CO2 emissions below 100g/km would have been enough to make one gasp and stretch one's eyes. They're still not exactly common, but there are several in production, one of the newest being the SEAT León Ecomotive, whose key figures in this context are 74.3mpg and 99g/km.The CO2 figure matches that of the original, and much smaller, Ibiza Ecomotive, which just goes to show how much development there has been in this field lately. It also means that, in this form, the León is exempt from annual Vehicle Excise Duty payments.Now, the important point here is that if the Ecomotive were fractionally more CO2-emitting - 101g/km, say - you would have to pay VED, but under the current system this would amount only to £20 per year. And it would be just £30 per year if the CO2 figure were as high as 119g/km. These are not large sums. What else in your life costs as little as £30 per year?The thing is, though, people are less prepared to spend money on tax than on almost anything else, and there are several successful examples of low-CO2 cars which require customers to pay much more up front than they would be required to cough up to the Exchequer if they had bought a more conventional model. I heard a representative of one manufacturer (not SEAT) make exactly this point when challenged about the apparent financial nonsense of the car he was promoting to the UK motoring media.Not all low-CO2 cars are expensive, though, and this is where we get back from the general to the particular. The León Ecomotive S originally went on sale priced at £15,090, and although that was a special deal the actual list price of £16,840 is still only £315 higher than that of the 104bhp 1.6 TDI on which the car is based. The better-equipped SE tested here costs £18,140, but the price differential is the same.If the only difference in running costs was the tax, it would be sixteen years before you could say, "Yes! I've done it! I've got my £315 back!" Sixteen years from now, owning a 99g/km car will be as socially acceptable as bear baiting and we'll all be driving cars powered by the laughter of small children (or, alternatively, our new insect overlords will be in charge and we won't be driving anything), so it's all going to be rather academic. Since the Ecomotive is also 7mpg more economical on the combined cycle than the 1.6 TDI, however, you could expect to be in the black a lot sooner than that.The improved "green" figures are the result of familiar tricks such as revised gear ratios, improved aerodynamics, Brake Energy Recovery and - for the first time on a SEAT - a start/stop system. Not bad for £315, I say.So, for its size and its fuel economy and its taxabilitylessness, the León Ecomotive is impressively inexpensive. On the other hand, it needs to be. Most of the Leóns I've driven over the last few years have been high-performance models such as the Cupra R reviewed here, for the simple reason that these are the most popular ones and SEAT has been extra specially keen for journalists to drive them.It's quite a long time since I drove a more humble León. I didn't like it then and I'm no more impressed now. Although it is very similar to the Volkswagen Golf, it seems about ten years older: it feels much less solid is and considerably noisier. And the silly window design and the fact that the interior mirror blocks out a remarkable proportion of the windscreen, elements which have bedevilled the León since day one, are less easy to accept when your attention isn't being drawn to storming performance.For a non-enthusiast who doesn't care much about cars as long as they're cheap to run, the Ecomotive is fine. In a wider context, it shows that the León's replacement is already long overdue. Engine 1598 cc, 4 cylinders Power 105bhp Transmission 5-speed manual Fuel/CO2 74.3mpg / 99g/km Acceleration 0-62mph: 11.5sec Top speed 118 mph Price From £18626.00 approx Release date 19/04/2010