German car manufacturers have succeeded in weakening new pan-European rules designed to reduce emissions from new vehicles. The heads of BMW, Volkswagen and DaimlerChrysler took part in last-minute lobbying to block proposals that would have forced manufacturers to make lighter cars with smaller, more fuel-efficient engines.

They demanded that José Manuel Barroso, President of the European Commission, withdraw a proposed new emissions standard, claiming that the German industry, which makes most of its profits from large, fuel-hungry cars, would be penalised unfairly The letter, a copy of which has been obtained by The Times, says that the new standard would force German car factories to close. It states: “These measures would amount to a massive industrial political intervention at the expense of the entire European, and especially the German, automobile industry.

“The direct consequence would be the migration of a large number of jobs from the automobile manufacturers and the supplier industry in Germany.”

The companies also persuaded Angela Merkel, the German Chancellor, to lobby on their behalf. The letter was sent on January 26, four days before Mr Barroso intervened in the debate over new car emissions to insist on a compromise that would benefit the Germans.

Stavros Dimas, the Environment Commissioner, had been seeking to reduce the average emissions from new vehicles to 120g of carbon dioxide per kilometre (g/km) by 2012.

The average across Europe in 2005 was 162g/km and it has fallen only slightly since.

Many Japanese, French and Italian models already produce less than 120g/km, including the Toyota Prius hybrid at 104g/km, the Citroën C1 at 109g/km and the Fiat Panda Multijet at 114g/km.

Britain’s car factories also produce large numbers of low-emission cars, including the Honda Civic, built in Swindon, which emits 139g/km, and the Nissan Micra, built in Sunderland, which emits 143g/km.

Under the compromise, to be announced on Wednesday, the commission is expected to accept the car industry’s demand for an “integrated approach”. This reduces the pressure on manufacturers to alter their designs by finding other ways of reducing emissions, such as increasing the take-up of biofuels, educating motorists about fuel-efficient driving and requiring roads to be smoother.

Environmental groups argue that these measures are much less certain to reduce emissions than changes in car technology and should be seen as providing additional savings rather than as an alternative.

A spokeswoman for Mr Dimas said: “We will see if there is some way to compromise. The proposal may not be the original one but it will still be better than any other part of the world.”

Jos Dings, director of Transport & Environment, a Brussels-based environmental campaign group, said: “What we are seeing is mindless scare-mongering from the German car industry. They are saying that makers of larger cars will have to close and thousands of jobs will be lost — it’s absurd.

“The problem has been that most carmakers have not cut emissions fast enough, and that’s why regulation is now urgently needed.”

Mr Dimas is seeking a binding target because the European car industry is failing to adhere to a voluntary agreement on reducing CO2 emissions. In 1999 the industry agreed to cut emissions to an average of 140g/km by 2008 but has no chance of reaching this level by then.