You can analyse it all you like but the idea behind this, Smart’s new ForFour, is to offer a car with the charm of a Mini, the practicality of a Polo and the engineering values of a Mercedes-Benz, Smart’s parent.

But what it must also do is build further on the sterling work of the original Smart City-Coupé (now rebranded ForTwo).

The car comes to us in the autumn with three petrol engines of 1.1, 1.3 and 1.5 litres respectively, and a 1.5 diesel with two power outputs. To look at its dual-tone colouring, detachable plastic panels and wacky styling, you’d think it just as innovative as the first Smart.

But scratch the surface of the ForFour and what you find beneath is startlingly conventional. And as many an awkward big brother has discovered when meeting his sister’s friends, you need more than flash clothes to look cool on a dance floor.

The ForFour’s creators could have played it visually safe, but then they could neither have called the result a Smart, nor charged so much for it. Even the basic 1.1 litre will cost around £9,500 when it goes on sale, which, when you can buy a 1.4 litre Honda Jazz for about £500 less, or a 1.4 litre five-door Polo for £500 more, sounds pretty steep. If you want a properly cheap version you’ll have to wait a few months for the ForFour’s cousin, the forthcoming Mitsubishi Colt, which shares 60% of the ForFour’s components.

Indeed, all three petrol engines (no diesels were available at launch) are from Mitsubishi, not Mercedes. But don’t scoff, because all are state of the art and offer power outputs, fuel consumptions and emissions that are best in class.

The four-cylinder 1.3 and 1.5 have reasonable manners, but the best is the little three-cylinder 1.1 litre version which provides outstanding performance from its 74bhp, combined with a characterful engine tone. The 107bhp 1.5 makes up in performance what it lacks in charm, but the 94bhp 1.3 has neither the charisma of the smallest engine nor the guts of the largest unit — a shame as it’s expected to be the bestseller. A five-speed manual gearbox is standard, a six-speed semi-automatic will also be available, though only posers are likely to find it preferable.

Think what you like of the ForFour’s exterior appearance, I find the inside far more pleasing — modern, stylish, cute and clever. Interior space is competitive and unusually flexible thanks to a split rear seat that slides fore and aft by up to 6in, and folds and tumbles forward to give excellent luggage space. The controls and instruments are laid out intelligently.

Less convincing is the driving experience. As mentioned, the engines are fine but the chassis is a let-down, providing little of the promised handling prowess, and a notably choppy ride, particularly around town. This means the ForFour is not much fun to drive, and this, for a car charged with taking a slice of the Mini’s action, is indeed a serious criticism. It has other strengths, such as disc brakes at each corner, standard stability control, antilock braking and four airbags, but these may not be enough to save the day.

What is beyond doubt is that the 1.1 litre is the best of the bunch, with impressive performance and great character. It will be interesting to try the diesels, as these are three-cylinder units too, but of Mercedes, rather than Mitsubishi, design.

The ForFour is a disappointment not because it is a conspicuously bad car, but because it fails to stay true to the values of the brilliant ForTwo. Smart’s boss, Andreas Renschler, told me Smart had to build it, as without the profits derived from its anticipated volume sales Smart will not be able to develop niche lines such as the ForTwo and Roadster. As a business case it is unarguable, but as a car it feels insufficiently special and looks too expensive to cast its net across the vast lake of its ambitions: Mini drivers will find it several streets behind in driving fun, while Polo owners will notice its plastic panels, contrived wackiness and unremarkable build quality.

Over dinner at the Smart’s launch I spoke to Renschler about how Fiat had got itself into such a terrible state. He said: “They concentrated on building bigger cars and consequently lost their focus” — an analysis with which I concur entirely. I hope that, 10 years from now, I don’t hear the same words from another industry executive about Smart.

The ForTwo gave Smart a set of quite exceptional values and, as a result, provided the brand with a unique opportunity. It will need much more careful management than this if it is not to be squandered.

VITAL STATISTICS

Model: Smart ForFour 1.3
Engine type: Four-cylinder, 1332cc
Power/Torque: 94bhp @ 6000rpm / 92 lb ft @ 4000rpm
Transmission: Five-speed, front-wheel drive
Suspension: (front) MacPherson struts, anti-roll bar (rear) coil springs, torsion beam rear axle, anti-roll bar
Fuel/CO2: 48.7mpg (combined) / 138g/km
Acceleration: 0-62mph: 10.8sec
Top speed: 112mph
Price: £10,500 (approx)
Verdict: Do not be deceived: the looks write a cheque the car can't cash