Key facts
Model tested: Fiat 500 TwinAir Lounge
Price: £12,065
Date tested: October 2010
Road tester: Rhian Angharad Jones

Fiat has long been at the forefront of engine innovation. The 500 TwinAir is an exercise in extreme downsizing, as it takes a 0.9-litre two-cylinder engine and creates the world's most efficient and least polluting mass-produced petrol engine.

The TwinAir has an ultra-efficient 875cc two-cylinder engine, returning 85bhp and 107lb ft of pulling power. It can go from 0-62mph in 11 seconds and on to a top speed of 108mph.

But despite its somewhat considerable power, it's capable of returning an average fuel consumption of 68mpg while emitting 95g/km of CO2 - this makes it 15 per cent more efficient and less polluting than the best-selling 1.2-litre petrol version, despite being 23 per cent more powerful.

With the addition of a five-speed automatic gearbox at a £730 premium, it can return 70.6mpg and emit 92g/km of CO2.

Fiat has achieved this by lowering engine weight and adding a gear shift indictor and a start and stop system, which temporarily cuts power to the engine when the car is stationary and in neutral to improve fuel consumption.

But the pace and efficiency come at the price of engine noise. While wind and road noise are impressively low, the hum from the TwinAir's two-cylinder engine is considerable. It's especially loud around town but things improve when cruising.

As with all 500s the chassis is responsive and fun to drive, although its characteristically firm ride is a little harsh around town.

The 500 TwinAir is available in three trim levels - Pop, Lounge and Sport - as well as two special edition models, the matt black BlackJack and the 500 byDIESEL from the well-known fashion brand.

---

---

Entry-level models come fitted with anti-lock brakes (ABS), electronic brakeforce distribution (EBD), five airbags (including driver, front passenger and side curtains), electric front windows and MP3 compatibility.

Lounge adds split-folding rear seats, a fixed glass roof, body-coloured electric door mirrors, 15-inch alloy wheels, USB connectivity and a leather multi-function steering wheel. Top-of-the-range Sport comes with 15-inch sport alloys and tinted rear windows.

With a starting price of £10,665, the TwinAir is £200 less expensive than the 1.4-litre petrol version in Lounge trim, but is expected to save buyers more than £1,500 in running costs - it's free to tax and will be exempt from the London Congestion Charge thanks to changes set for the new year.

The nearest alternative is the smaller Toyota IQ which, with a starting price of £10,000, it's capable of returning 65.7mpg and 99g/km of CO2, makes for a tempting proposition but can't offer the individuality of a 500 city car.

With its mix of affordability, eco-friendliness and looks, it's little wonder Fiat expect more than a fifth of 500 buyers to opt for the TwinAir version.