The A-Class is the people's Mercedes-Benz. Before it came along, you pretty much needed to be running a multi-national company to afford a Merc. Or, at least, you needed to be pretending to. Alternatively, you needed to be Gary Barlow, the owner of a top of the range S-Class, a car only marginally shorter than a battleship and twice as sturdy.

But then, in 1999, in an astonishing blow for democracy, the people from Mercedes came down from their castle, stood atop the barricades and offered the seething populace a car which was "merely" £13,000, if you didn't mind going without all the fancy bits. (Rest assured, a careful selection of on-board gizmos, aluminium trims and reversing sensors can boost the price of the car to an altogether more Merc-like £18,000, should you so desire. One wouldn't, after all, wish to alienate completely the long-term Merc audience, who like a bit of flash for their cash.)

The masses cheered gratefully at this political development. True, this was the smallest Mercedes anyone had ever seen - a crumb from the table, in some respects. But it was indisputably a Mercedes, complete with the badge and everything. There are currently more than half a million A-Class vehicles on the road in Europe and more than 80% of them have been bought by people who had neither owned a Mercedes before nor probably even dreamed of doing so. It's a victory for Class War.

Now the A-Class is back, and this time it's longer. Not as long as an S-Class, obviously, and thus not long enough for Gary Barlow. But definitely longer. On the face of it, you might think that wasn't a particularly smart move for a car which was all about being small and manoeuvrable. The idea of the A-Class seemed to be that you would stuff it with small children and sports equipment and then fly about town, blissfully immune to the routine urban diseases - streets narrowed to footpaths by parked cars, ruinously high petrol consumption, and parking spaces only suitable for wheelchairs.

Indeed, the watchwords for the original A-Class briefing were "short and tall" - a city-based imperative, and also a decision, incidentally, which was always going to leave the car struggling to be aesthetically appealing, given the received wisdom on these things. As a general rule of thumb, a beautiful vehicle is likely to be long and low; a vehicle that manages to be at the same time lanky and snubby is likely to be a parcel delivery van or, in more extreme cases, a competitor off Wacky Races.

The extent of the lengthening job on the new A-Class is seven inches - which may not sound like a lot, but which actually does go some way towards mitigating a feeling one had about the original model that, in its blockiness, it was to all intents and purposes a piece of Duplo on wheels.

Driving a car which resembled, in such an out and out way, a toy was likely to induce in the driver the paranoid sense that at any moment, a huge chubby hand could descend from the sky, pick up the car and fling it across the street. Heaven help your sports kit in that event.

It's amazing what a little extra length can do, then, because this longer wheel base A-Class seems to banish that nightmare altogether, allowing the car to have a slightly eased, almost graceful roundedness about it, rather than appearing abruptly sawn off at the back and tottering along on stilettos. But it's internally that the new length really adds up to something. Thanks to the wonder of maths, the additional seven inches translates into a load-space which is 11% more voluminous than on the original A-Class. We're talking about 1,865 litres of space, all in all, which is an awful lot of Coca-Cola. Maybe Gary Barlow would be interested after all.

There's more room for the passengers in the back, to the extent that they need not actually be intimate with one another to enjoy the offer of a lift in the A-Class. The car will genuinely, rather than comically, hold four adults; or you could turn the back seat over to three children without necessarily initiating a turf war. And in Rag Week my estimate is that the A-Class could comfortably contain 10 medical students.

For all that this is the Dinky Toy in the Mercedes range, it still drives like a Merc - to the extent that the engine responds in a quiet, unpanicked way to even your most furious demands of it, and to the extent that the car has a kind of stately solidity, which is altogether surprising in something that would fit in one of the bigger Mercedes' boots. Posh brakes, too.

If you want to complete the illusion, you can filter into your A-Class the titbits from higher up the food chain, such as an automatically dimming rear-view mirror. The big question is whether a car which, essentially, you are going to be taking to Sainsbury's and then on to the swimming pool necessarily cries out for walnut veneer. But, then, to believe this indubitably to be the case is to show all the signs of being a Mercedes-owner in the making.