The modular car is a radical concept: a vehicle that changes its form as you change your needs

The modern car is like a cautious man who carries an umbrella every day in case it rains. What is the point of under-using a twin- cam 16-valve 2.0-litre four-cylinder engine around town every working day when it is only once a month that you need the power it delivers? Why lug around an empty rear seat every weekday on the off-chance that you may have passengers at the weekend?

The main reason that the car is such a glaringly inefficient beast is because, for most of the time, we use a tiny portion of its potential. Most cars can seat five, do more than l00mph, accelerate from 0-60 in about 10 seconds, can easily break 40mpg, work happily at more than 50C and yet warm their passengers and their engines at -30. They also have absurdly big boots.

Few of these facilities - some legislative, some buyer expectation - are ever put to use. Until the car stops being a world machine (developed for all international markets, from the high-speed German autobahn to the deserts of Dubai) and resumes its role as a machine designed to satisfy the peculiarities of particular countries, these inefficiencies will continue. Being all things to all people is usually a recipe for wastefulness.

None the less, car makers can see the need for more flexibility. They talk about more "niche" cars: small-volume machines which can be made economically thanks to the wonders of modern mass-production. If Europe wants a baby car, but no one else does, let Europe have it. If the Americans want to continue with their dinosaurs, fine. As mass-production becomes more flexible, it is even possible to contemplate some cars being engineered and manufactured solely for individual countries once again.

The modular car is a more radical concept. A car that changes its form as you change your needs would clearly be the most efficient way of getting about. What is the point of lugging a 100-litre steel container (the boot) behind you all the time, when you use its capacity only for the summer holidays? Better to fit a boot when you need it.

The most sensible and practicable modular car proposal I have seen is the Opel MAXX. Opel (Vauxhall's equivalent in Germany) has designed a small city car using an aluminium frame, to which can be mated a variety of bodies - a conventional five-door hatch, a two-door coupe, a convertible, a pick-up, off-roader, van and even a taxi.

You order the basic car and the appropriate body style. If you want to change the body, or the interior, you can, while keeping the chassis and mechanicals. The new body simply clips on to the frame.

The MAXX is still in prototype form. Opel says it may go into production, although it must be at least five years away. It is confident, though, that the "tailor-made" concept shows great promise, and says one of the benefits of this "mix and match" approach is that cars can be made much more individual.

Mercedes foresees a time when you may simply rent body styles to attach to your car. Audi has even spoken of changing engines, as well as body styles, further improving flexibility. The only unchangeable would be the chassis.

Car makers know the modular car will happen. Demands for greater efficiency, and the simple fact that buyers now want more individuality from their cars, will see to it.