The challenge with the new SEAT Ibiza Ecomotive is to make the fuel gauge move. Go on - see if you can. Take it from Southend to Aberdeen, say, in second gear. With the handbrake on and a pallet of bricks in the boot. Any joy? Nope: the needle is still on “Full”.

Try again. Take the return journey, only this time towing a caravan, strapping a wardrobe to the roof and using only B-roads. What now? Well, yes, the pointer does seem to have moved a bit...no, hang on, I was wrong; it hasn't.

That's because the Ibiza Ecomotive is one of a slowly extending line of ultra-frugal and surprisingly cheap hatchbacks, designed to negotiate a workable truce between our consciences, our desire to travel, and a world in which oil, like money, may not be as readily available as before. Cars such as the Ecomotive and the VW Polo Bluemotion are redrawing the boundaries on how far we can go on a litre of fuel without being on a moped. They propose a situation, not long away, in which you drive off the dealer's forecourt with a full tank of petrol and then never pull into a petrol station again, ever.

Your local garage will carry on evolving aggressively, incorporating still further shopping facilities, cash machines, coffee bars and opportunities to purchase warm pastries and freshly microwaved hamburgers. But that will be a distant battle in a far-away country, as far as you are concerned, because you will still be driving around on the fuel your car first came with. The idea (perfectly natural to your peers) of stepping up to the counter and saying, “Pump number six, please - oh, and this loaf of bread and one of those disposable cameras,” will be completely alien to you.

I exaggerate, of course. But not much. The Ibiza Ecomotive manages to squeeze an eye-watering 74 miles out of a gallon of diesel. For a five-seat car, that isn't just being careful with fuel, it's developing some kind of rare allergy to it. Yes, you are, of course, going to have to refuel it at some stage. But let's at least say that if you're collecting tokens towards a set of whisky tumblers, the Ibiza Ecomotive is not the car for you.

Note, at the same time, the car's tiny, tax-dodging emissions figure - 99 g/km, for heaven's sake. That's less carbon dioxide than one slightly constipated heifer produces in half an hour of grazing (possibly). It's hard to know how much more tender towards the atmosphere a traditional car could be, short of running on a mixture of grass cuttings, rainwater and recycled breakfast cereal.

You would assume that there would have to be some kind of performance-based payback for all this ecomotivity - that, for instance, the car would accelerate from 0 to 27 mph in a little over four minutes and then not get any faster. Or that the body panels would turn out to be made from hardboard.

Quite wrong, though. The Ibiza Ecomotive doesn't look anything like a box of vegetables. It is smart and sporty. Its one drawback is an engine of a rare noisiness. It rattles and snorts the way that diesel engines used to, about 20 years ago, before the engineers got cleverer with them. But otherwise, the car has carpets, a stereo (of sorts), a steering wheel - all the things that one associates with cars that burn diesel at twice the rate.

Hats off, then. And yet it seems there has been no massive technological breakthrough - just a bit of clever tweaking. So what, you wonder, has the car industry been doing all these years?

The one slight surprise is that the Ecomotive distinguishes itself from other, more fuel-greedy Ibizas only by means of a relatively modest silver badge on the boot. When you've gone to all the trouble of saving the planet, you're going to want people to know about it. Maybe it should be possible to have the consumption figures sprayed on the bonnet. Or perhaps SEAT could suspend an optional steel halo above the roof.

Do consider the downside, though. Buy an Ecomotive and you will be stuck on 27 Nectar points for ever.

Top speed: 109 mph

Acceleration: 0-62 in 12.8 seconds

Average consumption: 74.3 mpg

CO2 emissions: 99 g/km

Eco rating: 9/10

One careful owner: Ebeneezer Scrooge

On the hi-fi: Ken Bruce

In the glovebox: Smints

Bound for: Leicester

Buy it because: there's a queue at the pumps

Price: £10,995

Marks out of 10: 8