Brussels - The difference between the stated fuel efficiency of cars and their actual consumption amounted to an overall 23.4 billion euros (27.3 billion dollars) for European drivers last year, according to a new study.

Car manufacturers have been accused of manipulating their fuel efficiency and emissions figures by exploiting loopholes in testing conditions that have allowed them to produce results during tests that look far better than what is achieved on the open road.

The gap between test and real-world performance has increased from 9 per cent in 2000 to 46 per cent in 2017, according to Transport and Environment, a campaign group.

Carmakers' claims "a scam"

Had real-world fuel efficiency increased in line with test values, it would have cost drivers across the European Union 150 billion euros less to tank up their cars during this period, the organization has calculated.

Germany accounts for 36 billion euros of this extra fuel expenditure, followed by Britain at 24.1 billion euros and France at 20.5 billion euros.

"Carmakers' claims of huge progress improving fuel consumption is a scam," said Greg Archer of Transport and Environment.

"Despite regulations to reduce Emissions, there has been no real-World improvement in CO2 (carbon dioxide) emissions for five years and just a 10-per-cent improvement since 2000," he added.

Calls for new tests

The campaign group wants laboratory testing to be replaced by more tamper-proof methods, such as real-world tests. But the European Automobile Manufacturers' Association, ACEA, argued that only lab values allow direct comparisons between different car models.

"Given that driving behaviour, traffic and weather conditions continue to differ from one situation to another, there will always be a difference between emissions measured in lab conditions and the real world," an ACEA spokesperson said Wednesday.

"Nonetheless, it is a matter of fact that technological improvements to new cars have resulted in major CO2 reductions in the past decades, leading to important savings for consumers," the spokesperson added.

Last year, following the Dieselgate emissions scandal around revelations that Volkswagen and other carmakers were manipulating tests, the European Commission introduced a new testing procedure, designed to be more thorough and produce more realistic results.

But there have been indications that this is also being manipulated to bring about less ambitious emission reduction benchmarks as the EU transitions from one system to another.