Sector: Lower Medium Price: £21,855-£24,800 Fuel: 54.3-62.8mpg CO2: 119-121g/km

Carbon-based taxation is driving rapid decline in CO2 emissions at the moment, and in turn resulting in some impressive factory figures from carmakers that could only have been fictitious until recently.

Certainly Alfa Romeo’s new six-speed, twin-clutch transmission (TCT), which is now available in the Giulietta, sounds this way. Fitted only to the 170bhp petrol and diesel engines, it uses Stop & Start to help bring emissions down, and works with the D.N.A. dynamic control switch to allow drivers to be as economical or enthusiastic as they want.

So huge are the CO2 reductions, that Alfa expects as many as 20-25% of the 6,500

predicted UK Giulietta sales this year to be fitted with this gearbox. Good going in a market where manuals have traditionally fared better.

For the diesel, TCT reduces CO2 emissions from 124g/km to 119g/km with fuel economy up to 62.8mpg. Gear changes are impeccably smooth, too, barely noticeable when cruising and kick-down is swift enough to not to require a pre-emptive tap of the steering paddles. But the extra 15kg up front does add to the already nose-heavy diesel Giulietta.

It’s the 1.4-litre turbo petrol that really sounds like the work of witchcraft though. Fuel economy here is best-in-class for a petrol engine at 54.3mpg, while CO2 emissions at 121g/km are 13g/km lower than the manual and 3g/km lower than the 104bhp VAG TSI engine.

There is a trade-off, though. The gearbox keeps the engine under 2,500rpm in normal driving, way out of its power band. And though smooth for cruising, the gearbox ends up scrabbling through a couple of gears before it finds enough power for rapid acceleration. Not a deal-breaker but it does make the petrol feel more lethargic than the diesel.

But at £1,350 over the manual, it’s an attractive way to get diesel-like emissions without paying the higher cost of upgrading to an oil-burner.