On the road: Dig the low emissions from this supercharged Micra

Micra prices range from £9,650 for the regular engine and from £11,150 for the hotter DIG-S version. This is more powerful, more economical and clean enough to be exempt from UK road tax and the London congestion zone charges.

So far this is a world first, supercharging a DIG motor. The plan was to get more power from the Micra’s 1.2-litre three-cylinder engine. The result is a boost of 22ps to 98ps – that is 96.6bhp in English – with the spin-off that all the versions, whether with five manual gears or the CVT automatic change, are rated and taxed at under 100g/km of carbon dioxide.

In France, customers buying a car producing less than 110 g/km receive a ¤400 bonus payment from the government, while in Holland cars such as the Micra DIG-S are exempt from the country’s BPM “green” tax, saving around ¤1,000 on first registration. There are also savings to be had in Scandinavia, with substantial tax benefits in Norway, Finland and Denmark available on cars producing less than 100g/km of CO2.

There are very few petrol engines that dip under the 100g/km level – usually the arena of highly efficient diesel models. Diesel can be very dirty. If I was running Transport for London I’d be wondering about dropping the congestion charge exemption for sub-100 diesels. Why? Because poorly maintained diesel engines belch out carbon-rich black smoke.

While trying the eco Micra in a city centre, I was behind a five-year-old family/company saloon. As it accelerated from the lights, the exhaust pipe billowed with sooty fumes. This is not unusual on relatively new diesels, although the mileage may be high and the servicing ignored. Dirty engines should be failed at the annual MOT. Cars under three years old and not subject to MOT scrutiny can still be dirty. It is worth mentioning that excess pollution from petrol engines may be less visible.

Nissan, of course, makes diesel cars but can present a business case for this Micra. To wit, with manual gears it has an official average of 65.7 miles a gallon, which is getting near diesel economy. With CVT gears it records 68.9mpg. Petrol is also cheaper to buy: around a 15p to 20p a gallon saving over diesel.

Then there is the extra cost of buying the diesel car, says Nissan. An example: a Toyota Yaris diesel 1.4 TR five-door at £14,760 has a £1,500 premium over a petrol Yaris TR 1.33. However, the Yaris diesel has much more torque than this Micra for better in-gear flexibility. The Yaris diesel records 72.4mpg and 104g/km. The petrol Yaris gives 52.3mpg and 123g/km. Ergo, the 65.7mpg Micra is not bad at all and saves on road tax and London charging. However, it costs £1,000 more than a normal Micra.

At resale, a diesel car will recoup some of its additional cost. The DIG-S on resale should also recoup its price premium over the unblown Micra.

Historically, superchargers were used to give an immediate power surge at low speed. Not in this case. Nissan has calibrated this unit to come on stream further up the engine power band. It means that to get the surge you must rev the engine hard, by which time the three-pot motor is sounding hoarse – as if it needs oiling, said my co-tester. Quite so.

The engine has stop-start ignition and uses the fiendishly complex “Miller cycle” for improved efficiency. If we compare a Micra Visia DIG-S with a standard Micra Visia, it gains nine miles a gallon and a reduction of 20g/km of CO2. The 0-62mph time of 11.3 seconds improves from 13.7 seconds.

The DIG-S costs an additional £1,000 in Acenta and Tekna trim, or an additional £1,500 for the entry-level Visia. This larger premium for Visia includes air conditioning – not fitted to the regular Visia. All DIG-S Tekna models have a parking gap size indicator, which gives a verdict on how easy it will be to park in the space. This is a first-in-class feature.

The facts:

It is: Nissan Micra DIG-S. Supercharged version of the petrol 1.2 five-door hatch, giving better acceleration and economy.

Emissions: All emit less than 100g/km CO2.

Automatic gears: Advanced lightweight CVT unit is a £1,000 option on Acenta and Tekna.

Prices: From £11,150.

Kit: All have some form of air conditioning, stability control, stop-start, auto door-locking with remote locking and a trip computer.

Verdict: It must appeal to anyone subject to the London congestion zone charge, who will recoup the price premium. The performance boost coupled with better economy is a selling point, though this is not a hot hatch and you pay an extra £1,000. The Indian Micra is a disappointment after the UK-built predecessor. It feels and looks built to a price, with a cheap plasticky interior and a poor ride on bad roads. I wouldn’t pay extra for the DIG-S unless I frequented the London congestion zone. Using the extra power of the engine will erode its mpg advantage.