MODERN cars may look sleeker than their forebears but they have put on so much weight that manufacturers now admit that Britain will fail to meet European environmental targets.

The average new car is almost half a tonne heavier today than it was 30 years ago, and improvements in fuel efficiency have virtually ceased.

Modern versions of old favourites, such as the Beetle and the Mini, have the worst problem with weight gain. The new Mini and the new Beetle are twice as heavy as the old versions. The new Land Rover Discovery, which weighs 2.5 tonnes, is now so heavy that it would be illegal to drive fully laden over many bridges.

The Society of Motor Manufacturers and Traders said that the extra weight was to blame for Britain falling well short of a European industry target for reducing emissions of carbon dioxide, the main global warming gas.

Emissions from new cars fell by only 0.4 per cent last year, the lowest reduction on record. With sales of 4x4s and people carriers soaring, average emissions could increase this year.

The motor industry pledged in the late 1990s to reduce average emissions from new cars to 140g of carbon dioxide per kilometre by 2008. Last year the average car sold in Britain emitted 171.4g/km.

The society’s annual environmental report said that gains in fuel efficiency were being undermined by new features that improve comfort and safety. Air conditioning and electric windows are now fitted as standard on many models. Side-impact bars, air bags and crumple zones also add weight but are now considered essential by drivers.

The extra weight requires more powerful brakes, which in turn add to the weight. Engines have also grown bigger to meet consumer demand for greater speed and acceleration. A basic new Fiesta now has a top speed of 101mph, compared with 79mph for the 1976 model.

The VW Golf has become not only half a tonne heavier over 30 years but also 2ft longer and 5in taller. VW said that it was obliged to keep increasing the size of its models to win customers.

A spokesman said: “The customer always demands more for less. We would be criticised if the new version was smaller than the old one.” He said that people also wanted more room inside cars. “People carry more and more stuff with them. They demand more cubby holes.” Jay Nagley, a car industry analyst, said that modern drivers had far higher expectations of comfort. “If you are stuck in a traffic jam you might as well be in a luxurious roomy car. And I’m afraid luxury weighs heavy.”

Friends of the Earth said that motorists should be forced to sacrifice their luxuries for the sake of the environment.

Tony Bosworth, the group’s transport spokesman, said: “Is air-conditioning really necessary when you could just wind the window down? And there’s no way you could describe electric windows as essential.”

Mr Bosworth said that the car tax system gave little incentive to buyers to choose cars with lower emissions. The vehicle excise duty rate for the worst gas guzzlers was raised by only £5 in the last Budget.

“We need to see the top rate more than doubling to £500 a year, with the rate for the most fuel-efficient cars reduced to zero,” he said.

A study by the Department for Transport last year found that a third of people would choose a greener model if the difference between the duty bands were doubled to £50.

The society said that the carbon dioxide target was for the entire European car industry and could still be achieved by improvements in other countries, even though Britain would fail to reach the required level.

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