Some ideas just have their moment. Stop & Start technology could well be on of them. I remember a certain German manufacturer inviting me for a drive in a prototype vehicle fitted with a system that would automatically cut the ignition when you rolled to a halt and restart it again when you prodded the throttle. That was the theory anyway. After three miles of crawling around the M1, I was left stranded in the middle lane, the starter motor chuntering pathetically as the battery had depleted its charge. Technology has moved on significantly since then and Citroen brings us a Stop & Start C2 with genuine 'real world' practicality.

The engineering is quite simple. Come to a halt and the Stop & Start system will cut engine power, effectively putting the car in a 'standby mode' when the vehicle stops at traffic lights and in traffic jams. Release the brake pedal and the engine instantly starts up again, with the vehicle pulling away once the accelerator is pressed. First trialled on the C3 model, the Stop & Start system proved so successful that it outstripped Citroen's most optimistic sales projections and is now available with the smaller C2. You won't get a whole lot of choice regarding engines and transmissions however: the Stop & Start system is optimised for the 1.4-litre 16v petrol engine used in conjunction with the semi-automatic 'SensoDrive' transmission, Citroen's electronically controlled manual gearbox. Priced at £11,295 in Rhythm guise, this C2 offers a realistic alternative to pricey hybrid models and outperforms them in many crucial respects.

So how is Citroen's technology any better than that which left me up the creek on the M1? The answer lies in a clever reversible alternator that acts much like a conventional alternator in normal mode. That is, it's driven by the engine to charge the battery, but when required, it can then act as a starter motor, driven by the battery to effortlessly restart the engine in just 400 milliseconds. This prevents the battery from having to do all the work itself. A low inertia starter motor also helps preserve charge.

"The C2 Stop & Start offers a cheap, simple and painless way to make significant efficiency savings"

Citroen claims that the 'Stop & Start' system has reduced fuel consumption by 10% for city driving, 6% in a standard combined cycle and up to 15% in heavy traffic. All this sounds reasonable, as does the fact that CO2 emissions are reduced by a similar proportion. You could also argue that widespread adoption of 'Stop & Start' technology would help to improve the quality of life in cities, since drivers and the urban environment would benefit from total silence during the many times vehicles are stopped. One caveat: it's well worth remembering that pedestrians aren't used to these sorts of cars and may well walk out in front of you, assuming you are parked.

And the Sensodrive gearbox? Well, it does make this C2 supremely easy to pilot in urban traffic. The gearbox features a mode whereby it defaults to a conventional automatic transmission, thus saving you the bother of shifting yourself. When the road opens up, you can switch it to sequential mode and flip up and down the gears using paddles behind the steering wheel or the centrally-mounted gear lever. It's not one of those clever clutchless manuals like an Alfa Romeo Selespeed or a Vauxhall Easytronic system - there's still a conventional automatic torque converter - but it does offer three different programs (Normal, Sport & Snow) as well as that fully automatic mode. A top speed of 105mph means that typical motorway cruising speeds aren't going to leave you looking like a shell shock victim after an hour behind the wheel, although acceleration isn't that brisk - you'll need 13.9 seconds to hit 60mph.

Sit inside a C2 and you're not constantly reminded of your penny-pinching ways. It feels cheeky, modern and agreeably sophisticated. Based on the SX trim level which already features air-conditioning, a CD stereo, electric front windows, power steering, driver's seat height adjustment and front lateral airbags as well as clever sliding and folding rear seats, the Stop & Start piles on around £1,000 of extra kit. This includes rear parking sensors, automatic air conditioning, automatic headlights and wipers, lateral airbags and electric heated door mirrors.

Although it shares its chassis, drivetrains and a number of body and interior parts with the C3, don't think of this car as merely a scaled down version of Citroen's spherical supermini. The styling marks a different direction with a C3-style bulbous nose allied to a far edgier, angular back end. Although to some it might look like the results of two design studies fused at the door pillars, it's certainly distinctive. The side windows adopt a staggered line while the rear haunches blister out in a purposeful fashion and the latest models can be identified by a clear section in the tail-light clusters.

Although the C2 Stop & Start may seem a slightly low tech way of achieving improved efficiency, sometimes the simple ideas are the most effective. Do the sums and I'd be willing to lay money on the fact that this car would work out cheaper to run than a hybrid like a Toyota Prius or a Honda Civic IMA over the course of three years. After all, isn't getting ahead in the city all about working smarter not harder?