When it comes to saving the planet, who do we look to? The scientists? Yes, most of them. The politicians? Hmm, maybe some of the more sincere ones. OK, hardly any. Showbiz stars? If you say so.

The car industry? Yes, actually. Cars today are cleaner and greener than they have ever been. Years ago, the auto industry (in co-operation with the even more maligned oil giants) got rid of lead in petrol, most of those sooty carcinogenic bits in diesel and various other nasties. I admit a great deal of this has been as a result of official pressure, notably from the European Union, but the technical achievement is staggering. Who knows what the car makers will do next? We already see ever more efficient petrol and diesel/electric hybrids, hydrogen fuel cells and other energy sources (such as renewable biofuels), and more cleaner, greener kit is on the way. Richard Bremner writes about some of it on this page.

After 120 years, however, it would be a shame to junk the dear old internal-combustion engine. It still has life and development potential in it, as Volkswagen proves with its curiously named Polo BlueMotion ( below). This takes the existing Polo’s admirable economy to a still higher pitch; official figures suggest that 72mpg is possible. You can, if the hype is justified, drive from London to Edinburgh on £20 of fuel.

This Polo BlueMotion features revised aerodynamics (grille, tailgate spoiler), low kerb-weight, hard compound tyres to reduce rolling resistance, lightweight wheels, and an advanced three-cylinder diesel engine that is linked to optimised gear ratios for high economy and low emissions. They’ve “added lightness” and removed strain from the engine by deleting the air conditioning, the door-mirror electric motors and the remote central locking. You could live without those fripperies, though, surely?

So this Polo, a proper four-seater with the usual “baby tank” appeal, will deliver 102g/km of CO2. That’s lower than the two main hybrid offerings, the admittedly larger Toyota Prius (104g/km) and the Honda Civic Hybrid (109g/km), and the petrol Smarts (116g/km). Nor will you have to refuel much: the theoretical range of the Polo BlueMotion exceeds 700 miles.

This Polo, however, is no fireball. The 1.4-litre diesel unit makes its presence very well known, and I wouldn’t even bother trying to get frisky with it. It keeps up with congested modern traffic, urban and motorway; it should top 100mph, which is probably all you ought to be doing in it (and going that fast wastes a lot of fuel).

All this economy comes at a price, too: about £12,000 when it arrives in showrooms this summer. For much less (£10,675), you can buy the conventional 1.4 TDI 70S model, giving an average 60.1mpg. So you gain 10mpg for about £1,500, and that doesn’t make much financial sense. Maybe in the very long run, and when the price of fuel has doubled again, and when you’ve done vast mileages in your Polo BlueMotion, it’ll be worth it. Maybe.

Then again, you might consider one of the cute-sey Citroën C1/Toyota Aygo/Peugeot 107 trio, which can return a claimed 68.9mpg and cost about £4,000 less. The petrol versions of these three return a very respectable 61.4mpg (combined) and cost about £2,000 less.

So the car industry really has tried to make greener products – but do we have to pay so much? Why is the green premium so high?

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