Mini begat Mini, begat new Mini...

BMW's updated classic is itself getting a facelift. John Simister takes the new-generation prototype for a spin

Mini is defined very closely by the way it looks. You couldn't create a brand-new Mini and have it looking like a Nissan Micra; it must look like a Mini, otherwise it wouldn't be one.

That could make life difficult for BMW, because one day it might need to replace its fantastically successful Mini, of which 831,412 have been sold, with a new one. In fact, that day will be in September. The current Mini is a remake of an automotive icon, but such has been its success that it has become an icon in itself. The new one must build on that following while staying true to the original Issigonis look.

And it does. I've just been driving some pre-production prototypes at the Zandvoort race circuit near Amsterdam (the scene of the famous Cosworth DFV engine's first-time-out victory in Jim Clark's Lotus 49, 1967 Dutch Grand Prix), and I'm delighted to report that the Mini-ness is fully intact. The new-generation car has all the appeal of the current one, updated for a changing world and new emissions and safety regulations.

But why change the current car? Well, it was introduced five years ago and BMW wants the Mini (built in Cowley, Oxford, don't forget) to stay on top of its game.

At first the changes seem no more than a mid-life facelift. Look more closely, and you'll see that every exterior panel has changed a little, that the car is 60mm longer and that its waistline has risen by about 20mm. The bonnet is still a big one-piece panel that includes the front wings, but it now leaves the headlights and the front wheelarches behind when it opens.

With the bonnet open, you can see the most important change: a new engine. The old one, cheaply made in Brazil by a BMW-DaimlerChrysler joint venture, has been replaced by another joint-venture unit, featuring the highest of high technology and co-developed with Peugeot, which will use it in future 207s.

The Mini versions are made at the Hams Hall factory near Birmingham, and will start off as a 120bhp unit with Valvetronic variable valve opening (so no conventional throttle) for the Cooper, and a 175bhp turbocharged, direct-injection version for the Cooper S. Both engines are 1.6 litres and gain 5bhp (and a lot more usable low-end pulling power) over their same-size predecessors. A smaller-capacity engine is likely to follow for the next entry-level Mini One, although the current version and convertibles will continue for a while.

The new engines are also more economical, and the cars are slightly lighter than the old ones, thanks to greater use of aluminium.

Time for a run. My test car still wears some disguise to cover the detail changes, especially inside where the dashboard and centre console are partly hidden under plastic sheet. But I can still see the central speedometer, grown to the size of a small dinner plate and containing the audio information and switches in its lower third.

Heater controls are arranged in the shape of a Mini badge, and some reshaping of the seats has released some welcome extra space in the back. Insert the "smart" key - it contains all the driver's preferences, including radio station presets, press the starter button and we're off. First there's a slalom and turning test among cones, in which the Mini - it's a turbocharged Cooper S - proves tidy and agile.

There's a new electric power-steering system which has a fractional response lag when I'm flicking through tight turns, but it's accurate and feels convincingly solid.

And now on to the track. The key difference between this new Cooper S and the old one, when driving, is that turbocharger. The previous S had a supercharger, whose whine made the car sound like an original Mini and which I rather liked. It gave a near-instant, and accurately controllable, response to the accelerator, even at low speeds but was not great for fuel efficiency. The new turbo engine feels softer in its response, especially from low speeds where you have to wait for the boost to build up.

Once you've adapted to that, the engine proves impressive with its muscular power delivery. Even quite tight corners are better in third gear, using torque rather than revving hard in second gear. I miss the instant response of the old car, though, an attribute central to a Mini's personality.

Also, the new Mini is less keen to flick its tail out when provoked in a corner. This attribute helped give the old car its chuckable-Mini feel, but some people found it worrying. The new one flies round corners with great zeal but forces its front tyres to work harder, so there's less of a feeling of subtle and intimate car/driver interaction as steering is played against accelerator.

All this might feel quite different when we try the new Mini on the road. We'll be back with a full report.