Greenpeace has slammed Volkswagen's environmental record by claiming that the giant carmaker has stalled on fuel efficiency gains and is attempting to thwart an EU plan to dramatically lower CO2 emissions by 2020.

In its report, 'The Dark Side of Volkswagen', Greenpeace complains that Europe's largest car manufacturer has purposely restricted its most fuel efficient engines to a tiny minority of vehicles, and then drastically increased the price for consumers.

Volkswagen is hardly alone in adopting that business policy, but the environmental group says the problem goes further. It says that the company is lagging behind its rival, citing a 7.8 percent drop in average emissions per kilometre compared to reductions of 18 percent and 14 percent for BMW and Toyota.

Even more damning from Greenpeace's perspective is Volkswagen's apparent opposition to laws which it believes will limit climate change.

"VW is at the heart of a group of companies lobbying against new laws which we need to cut CO2 emissions, reduce our oil use and protect places like the Arctic from climate change," claimed the organisation.

It has highlighted Volkswagen's objection to the targeted 30 percent drop in overall emissions from 1990 levels (the manufacturer supports a 20 percent reduction), as well as its criticisms of the EU's automotive emissions target of 95g/km CO2 by 2020.

The firms investment in plug-in hybrids and future EVs appear to have cut no ice with Greenpeace, which said, "The truth is that the Volkswagen Group has lagged behind its competitors for years. It only stepped up progress on CO2 reductions once a legal framework was put in place that forced it do so. It has shown no ability or willingness to voluntarily deliver the innovation or technology changes required.

"Now Volkswagen is openly opposed to the agreed 2020 standard that would benefit motorists, the economy and the environment."

It seems unlikely that the world's largest eco-crusader will let its assertions slide either. Following hard on the heels of the 24-page report, Greenpeace is planning a social media firestorm which will include a parody of Volkswagen's own spoof Star Wars advert. Click below to watch.