In the modern panoply of environmental evils, none can be so insidious, nor have corrupted our minds quite so profoundly, as the Western throw- away culture.

Consumer "durables" are now usually anything but - from houses to white goods; from clothes to other everyday items (telephones, for instance, are now reckoned by the the New Economics Foundation to have a typical life of only three years). It is a corollary of our obsession with price rather than permanency. It is also an upshot of fashion: the modern phenomenon that replaces need with want. Consumer goods are often designed to be consumer "bads" in no time at all.

Oddly, about the only industry that can hold its head up and plead "not guilty" is the motor business, so rarely the environmental good guy these days. From tyres to bodies, from motor oils to brake pads; they all last longer. Even a gallon of petrol goes further than it used to, thanks to improvements in fuel formulation.

While the makers of cameras, fridges, irons, houses, shirts and shoes (and so on) can look forward to increasing turnovers, the greater longevity of cars presents the motor industry with a problem. How do you persuade punters to trade in their perfectly good cars for new ones - when the new one is little different, shinier paint and snazzier options notwithstanding?

The recent recession also did not do the car makers any favours. In Britain, many companies kept their cars for nearer five years than the usual three. And what did they find? Surprise, surprise: the five-year-old cars went perfectly well.

Needless to say, the motor industry is aware of the problem. It is one of the reasons why car firms' marketing budgets get ever higher. There is the usual big-budget advertising campaign to launch "new" models which, in many cases, are merely facelifts complete with minor mechanical make- overs. There are the usual trim and colour changes every year; sometimes there are important safety upgrades, such as airbags and anti-lock brakes.

The car makers' lobbyist, the Society of Motor Manufacturers and Traders, is also exerting pressure on the Government: it wants state incentives to scrap 10-year-old cars (if the owner then buys a new one), on the basis that it would improve the environment. Improve the air quality in cities, it might do; improve the environment in the wider context, it probably would not. What about the energy costs involved in making new cars and in their transport, and the environmental cost of scrapping the old cars?

The recent car advertising hype about recyclability was another roundabout way of encouraging us to change. It salved our environmental consciences - "it really is fine to keep changing cars because cars can, in effect, be used all over again" was the message. An over-reliance on recycling in any industry is bad. It encourages the disposable culture, because we think that recycling does the planet a favour. It does not. It is merely better than dumping the object into a landfill site. Much better to keep using the product in question longer. (The recent recyclability boasts from the car makers were all tosh, anyway. Modern cars are far less recyclable than old cars, because they use so much more plastic.)

The biggest new ace up the car industry's sleeve, in its quest to encourage us to keep changing cars, has been to jump into bed with the masters of planned obsolescence: the electronics industry. Cars use more and more electronics to meet emissions legislation and to control everything from automatic gearboxes to alarms to anti-lock brakes. The increased use of electronics has made cars safer and better. But it also reduces their practical working life - just as the industry gets the important mechanical bits right.

The new BMW 750iL, tested on this page last week, is a great example of a car that could last for at least 20 years - yet will not because of its reliance on electronics. Although the body, suspension and engine are near unburstable, will it really be economic in a decade or less? Its owner will have to spend a couple of thousand pounds on new electric motors for the seats, a new electronic brain for the engine, and various other microchips and computers that are littered around the car controlling crucial functions.

Many cheaper cars, which nowadays also increasingly rely on electronics, will probably be scrapped after about 10 years. Important electronic components will not be available, or will be too expensive to repair. Otherwise good cars will be made redundant.

Is this a cynical ploy by the motor industry to encourage us to change our cars more frequently? Or is it the fault of the electronics makers for failing to supply parts which will last, or be capable of service and repair in a decade? It is probably a bit of both.

Either way, if you are buying a car to last - and the longest-lived makes are probably Mercedes and Volvo - it makes sense not to order too many electronic options. Keep it simple when you order, keep it clean and well serviced, and your new car should last for an easy 15 years. Of how many other modern products can that be said?

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