MPs have launched an inquiry into the testing of new road vehicles following the diesel emissions scandal.
Volkswagen admitted in September that it had fitted software designed to cheat emissions tests for nitrogen oxides in 11 million diesel vehicles worldwide, including almost 1.2 million in the UK.
The crisis deepened earlier this month when it emerged that the German-based manufacturer had understated CO2 emissions and fuel consumption for 800,000 vehicles.
The House of Commons transport select committee has launched an inquiry into how vehicles on the UK's roads are tested after it was told by VW's UK boss Paul Willis that "it is widely recognised" current testing "is not fit for purpose".
He wrote "its deficiencies are recognised" because of the difference between laboratory results and real world driving.
Committee chair Louise Ellman said: "The Volkswagen scandal has raised serious concerns about whether vehicle type approval testing is fit for purpose.
"We heard evidence in October that the gap between emissions detected in test conditions and those detected in the real world is significant. The testing procedure is clearly inadequate.
"The EU is taking steps to move towards real world driving tests. The current proposals have been criticised for giving too much leeway to motor manufacturers.
"It is essential to examine these allegations and to ensure that the Government and EU take action to restore public confidence."
Environmental groups expressed their anger after EU countries agreed 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 short-term improvement of diesel cars.
The select committee wants to hear evidence on the effectiveness of current testing arrangements, the impact of real world testing and comparisons with countries such as the US and markets in Asia.