The UK Transport Secretary knew car manufacturers were falsifying the results of their emissions tests to comply with regulations up to a year ago but failed to act on warnings.
The Department of Transport received a report from the International Council on Clean Transportation warning of a compliance issue last October, a spokesman said.
The same report helped reveal that Volkswagen was falsifying the results of tests in the US.
The report found "strong evidence of a real world nitrogen oxides compliance issue for recent technology diesel passenger cars, both for the EU and US vehicles".
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Patrick McLoughlin, the Transport Secretary, reiterated calls for the the European Commission to investigate vehicle emissions on Tuesday.
The Vehicle Certification Agency, which oversees emissions test in the UK has since said it will re-run laboratory testing to compare to real-world emissions.
The ICCT tested 15 vehicles and found that they were pumping out seven times the legal limit for nitrogen oxides, which can cause respiratory problems and premature death. The UK Government has estimated that nitrogen oxides and particles associated with diesel emissions may cause up to 50,000 premature deaths a year in the UK.
The ICCT called for urgent regulatory action in Europe, where there are more diesel cars than anywhere else in the world thanks to incentive schemes in the 1990s designed to reduce carbon emissions more strongly associated with petrol vehicles. Diesel-powered vehicles emit up to 20 per cent less CO2 per kilometre travelled.
Andrew Pendleton, head of campaigns at Friends of the Earth, said the UK probe must be the start of a diesel clean-up on Britain’s roads. “UK air pollution kills 52,000 people prematurely each year and diesel fumes are a major contributor, so the government and regulator must not tolerate any discrepancy between the laboratory and open road,” Mr Pendleton said.
