Until recently, there was very little choice when it came to green cars. You could buy either a supermini with a very small engine, or a hybrid like the Honda Civic Hybrid or Toyota Prius, both of which use a battery powered motor alongside a petrol engine to get maximum mpg and reduce C02. If you wanted a car with great driving credentials, you were out of luck.

So its hats off to four cars makers who, in the last year or so, have simply adapted technology they use already to bring us low-CO2 versions of their exisitng cars, with only a minimal increase in price.

> Seat Ecomotive
> Volkswagen Polo BlueMotion
> Ford Focus Econetic
> BMW Efficient Dynamics

The first car to come from Seats own green brand is the Ibiza Ecomotive. The super efficient 1.4 litre diesel emits 99g/km, identical to the Volkswagen Polo BlueMotion. Thats no surprise, because both are very similar under the skin. Improved aerodynamics, longer gear ratios and low-rolling-resistance tyres all contribute to the Ecomotives green credentials. It wont just save money at the pumps, either : emissions are so low, theres no road tax to pay.

The Ibiza Ecomotive goes on sale this spring, with the Leon Ecomotive joining the line-up by the end of the year.

> Get a free car leasing quote for the Seat Ecomotive

The Volkwagen Polo BlueMotion can lay claim to the best economy and the lowest emissions of any car currently on sale. Basic models deliver a remarkable 74.3mpg on combined cycle, although better-equipped versions will use a little more fuel. CO2 emissions of just 99g/km are lower than those of any hybrid.

BlueMotion version of the Golf, Golf Plus, Jetta, Passat and Touran have also been developed, while there are rumours that a BlueMotion version of the new Tiguan 4x4 is on the way.

High-efficiency diesels, more aerodynamic bodywork and low-rolling-resistance tyres combine to cut carbon output, while particulate filters make sure that the local air quality is taken care of, too.

> Get a free car leasing quote for the Volkswagen Polo BlueMotion

Several car makers have founded their eco-brands on conventional diesel technology, tweaked to the nth degree to maximise efficiency. Fords is called Econetic, with a wide range planned. The first of these is the Focus Econetic, which was first shown to the public at the Frankfurt Motor Show last year and is now on sale. Under the bonnet is the familiar 1.6 litre TDCi engine, but with changes like its improved efficiency, using low drag tyres and even low-viscosity transmission oil all add up.

The result is an impressive CO2 output of 115g/km and 65.7mpg from the more powerful 110bhp unit. That means it ekes out 6.8 mpg more than a standard Focus diesel, nearly a 12% improvement.

> Get a free car leasing quote for the Ford Focus Econetic

Forget your hybrids and hydrogen fuel cells - BMW reckons theres still plenty of life in the internal combustion engine yet. No fewer than 22 petrol and diesel models from the 1 series, 3 series, 5 series and Mini ranges have been given the Efficient Dynamics treatment, and all emit less than 140g/km of CO2.

Measures such as Start-Stop technology, regenerative braking and low-rolling-resistance tyres also make the most of every last drop of fuel. Similar measures are also applied to the X3 and X5 4x4s.

> Get a free car leasing quote for the BMW Efficient Dynamics