A laboratory test has reportedly found that Volkswagen diesel cars fitted with sophisticated software can cheat European emissions tests as well as those in the US.
BBC Panorama made the claim after taking a vehicle to an accredited testing lab in the Czech Republic.
VW has admitted fitting 11 million vehicles worldwide - including almost 1.2 million in the UK - with defeat device software.
It accepts this was used to rig pollution tests in the US, but it has not previously been known whether this also happened in Europe.
Panorama put a VW Passat Blue Motion diesel - with a defeat device - through the standard Euro 5 emissions test that the model would have passed before going on sale in Europe.
It found that the car emitted 167mg/km of nitrogen oxides and dioxides (NOx), which is below the official limit of 180mg/km.
But the investigators then tricked the software into believing the vehicle was no longer in a lab by accelerating hard and then repeating the Euro 5 test with a hot engine. The car failed by a huge margin, emitting 435mg/km of NOx.
VW told the programme: "With this software, it was possible for the vehicle to recognise laboratory test conditions and the engine control could switch over to emitting compliant nitrogen dioxide levels during the test cycle.
"This would have been the likely condition in your test. As you ran the second test immediately afterwards, the vehicle did not recognise this as a test condition and changed its emission strategy."
EU countries agreed last month to allow diesel cars to pollute more than double the current legal limit as part of a package to introduce real-world emissions testing.
Cars will be allowed to emit up to 2.1 times more air pollution in real-world tests than the legal limit.
The European Commission said this was because of ''technical limits'' in the possible short-term improvement of diesel cars.