Audi has been a dominant force in the mid-range car sector at the quality end. Now the new A4 has added style, space and economy. Our Motoring Correspondent, Michael Moroney, drove the new Audi A4 TDI and he's impressed.

Now that the VRT changes are settled into place its worth comparing the differences between petrol and diesel powered cars in a similar band.

That's why I opted to take the new Audi A4 TDI to the road, not long after I had driven the A4 with a 1.8 litre TFSI petrol engine. So what's the difference is the obvious question?

In specification terms there is little difference between the two cars. In appearance terms they are identical, with similar features, wheel sizes and 205/60 R16 tyres and the Audi design appeal remains the same.

As mentioned in the previous A4 report this new model is bigger and feels more spacious than the model that it replaces.

So this is a car that's both attractive and comes with a high safety specification and the bonus of thrifty diesel power.

Audi has a new 2.0 litre turbo-diesel engine under the bonnet of the new A4. The engine develops a massive 143bhp, which is impressive for a diesel car in this size category.

What's even more impressive than the engine power is the torque output. This new A4 comes with 320Nm of torque and that's what gives it good acceleration. The acceleration figures for the A4 TDI show that it can achieve a 0 to 100km/hr acceleration race in just 9.4 seconds.

That's slower than the petrol powered equivalent while rated as amongst the fastest in the sector and 2 seconds faster than the previous 1.9 litre TDI A4.

The real diesel bonus comes to the fore when you look at the economy and CO2 figures. The 2.0 litre TDI A4 delivers an economy figure of 5.5 litrs/100km, that's 22% more efficient than the 1.8 litre TFSI petrol model and counts as a saving in your pocket.

Audi has reported recently that it has surpassed even this performance. During a test in Austria and Switzerland the company returned a figure of as low as 3.32 litres/100km, which equates to a CO2 figure of just 88g/km.

This standard test car economy level brings with it attractive and low CO2 rates. The diesel model comes with a rating of 144g/km, which is low for a car engine of this size. Convert this to motor tax rates and the new A4 diesel is in the Band C giving a competitive €290 annual road tax rate. That's €140 per year less than the petrol model.

The CO2 rating is equivalent to some of the smaller diesel engine cars in the sector, such as the Renault Laguna 1.5 litre and the 1.6 litre Peugeot 406.

The difference with the new A4 is that it has pace as well as a good economy figure. Compared with the 1.8 litre petrol powered option, the new diesel model while slightly less powerful, comes with 25% more torque.