BMW Mini Cooper D

Once upon a time ‘diesel’ was a dirty word. We dreaded the stink of the fumes ­pouring out of noisy, brutish lorries and buses. But those days are long gone.

With technological advances over the past two decades, the diesel engine has had a dramatic make-over. Today, 40 per cent of cars on our roads are run on diesel, and this alternative to petrol has some real attractions.

For a start, a diesel car will probably last a lot longer. It can easily put more than 250,000 miles on the clock during its lifetime – not many petrol cars can hang in there for that long.

A diesel engine is more ­robust than its petrol counterpart and quicker to warm up on a cold day. Its greater torque gives it good pulling power and makes for less gear-changing – a real advantage in everyday city driving.

More importantly, diesels are about 30 per cent more fuel efficient than petrol cars.

“You can get on average 32 mpg from a petrol car and 45 mpg from a diesel car – ­although some do a lot more than that,” says Paul Watters, head of public affairs for the Automobile Association.

“There’s no doubt ­diesel is more economical to run.”

And you can forget the old idea of diesel vehicles ­being sluggish. “Modern ­diesel engines are pretty nippy. They’re turbo charged, which ­enhances their performance, especially in the higher gears used in motorway driving,” says Watters.

As for its green credentials, diesel is less polluting than petrol. It contains no lead and emits fewer regulated pollutants than petrol cars.

While it’s true that diesel emits more sooty particulates, cars that run on it now come fitted with filters to capture them.

In fact, diesels are among the most eco-friendly cars available in the UK.

The website greencarsite.co.uk has a list of 57 vehicles with CO2 emissions of 120g per km or less –meeting the EU standard for air pollution emissions – and 41 of them are diesel.

The only two which come in at just under 100g per km, making them road tax ­exempt, are diesels: the Seat Ibiza 1.4 TDI 80PS Ecomotive and the Volkswagen Polo Bluemotion 1.4 TDI 80PS.

"There’s no doubt ­diesel is more economical to run"

So, one might ask, what are the drawbacks? Well, a diesel car will almost certainly cost you more to buy, mainly ­because the complex engine itself is more expensive.

And then of course there’s the actual fuel. While it is just as readily available at the pumps as petrol, these days diesel is more pricey than it was (about 11p per litre more than petrol) because it is in shorter supply and it’s all imported.

So you need to clock up a pretty high mileage each year to get the full benefit of diesel’s superior mpg performance.

And despite rocketing sales of diesel cars in recent years to the point where they are ­almost on a level with petrol motors, What Car? editor Steve Fowler doesn’t see them overtaking petrol any time soon.

“If anything, the pendulum could be swinging back petrol’s way,” he says. “Yes, diesel cars are more fuel-efficient, have a low CO2 output and are therefore more tax-friendly. But the premium you pay for diesel fuel means you have to drive even more miles per year to make the extra costs of buying a diesel car worthwhile. And if anything, people are driving fewer miles at the moment.

“However, today’s diesel cars are a world away from the tractor sound-alikes of a few years ago – they’re fast, ­refined and not as smelly or smoky as they used to be. In fact, a diesel-powered Audi won the Le Mans 24-hour race this year!”

It doesn’t get much sexier than that.

Six greenest cars on the market

• Seat Ibiza 1.4TDI £10.995

• VW Polo Bluemotion 1.4 TDI £12.150

• Mini Cooper D R56 £14,420

• Citroen C1 1.4 HDi £9,225

• Mini Clubman Cooper D R55 £15,405

• Skoda Fabia Estate 1.4 TDI £11,495