By Roger Harrabin
BBC environment analyst
The cost of "gas-guzzling" cars could soar in five years' time under plans from the European Commission.
Bigger cars may find it harder to cut their emissions cheaply
The commission wants to impose mandatory efficiency standards on all new vehicles sold in Europe as part of a master plan to combat climate change.
Some of the UK's best-known carmakers could be hardest-hit.
Currently the EU has a voluntary agreement with motor manufacturers - but they have infuriated the commission by missing their target by almost 50%.
Environment Commissioner Stavros Dimas now wants mandatory standards that will allow the average car to emit just 120 grams of carbon dioxide (CO2) per kilometre.
That would mean a 1.6 litre petrol Ford Focus would need to cut emissions by a third to qualify as an average vehicle under the new regime.
Car manufacturers will be able to average out their overall CO2 targets over their entire range of vehicles.
But it is clear that heavyweight luxury cars like Rolls-Royces, Bentleys and Range Rovers will have to invest far more in costly low-pollution technology to reduce their emissions than smaller lighter cars.
Mr Dimas wants people to wage war on climate change
Britain's Society of Motor Manufacturers said the plans threatened jobs in the car industry, particularly for specialist manufacturers.
They forecast that the plan would add as much as 2,500 euros (£1,650) to some cars, and they warned that European makers would lose out to imported models.
Mr Dimas said the new rules would apply equally to imports, adding that the EU would offer tax breaks to carmakers to help the transition to lower-emission vehicles.
He admitted that costs would rise for buyers of top-of-the-range vehicles, but said higher costs for the average consumer would be outweighed by fuel savings over the life of the vehicle.
The proposals underpin the commission's recently unveiled climate masterplan, and will be discussed by politicians shortly.
The plan may face political opposition, but climate is changing the industrial landscape in a way that may persuade Europe's politicians that it is kind to be tough on their own carmakers.
California has set a benchmark for fuel-efficient vehicles that will make it increasingly hard for the manufacturers of gas-guzzlers.
Detroit's carmakers - traditional opponents of fuel efficiency standards - are now finding themselves trailing in the race to make cleaner vehicles.
Mr Dimas told BBC News that people should start talking about climate change as a war.
It could lead to the death of millions of people, and it could transform the world economy into a war economy, where every sector was involved in the fight against climate change.
As a result, he said rising emissions from transport were a problem that had to be tackled.