CURRENT vehicle emission testing is inconsistent and inaccurate, says a critical report from the National Audit Office. Its latest report for Parliament claims that 10%-20% of vehicles are driven every day with illegal emissions, and suggests that testing has only improved the emission levels of a quarter of the vehicles on UK roads.

Sir John Bourn, head of the NAO, said the current test had 'technical limitations' and many garages had practical difficulties in applying the test. He reports that 'the diesel test can produce inconsistent results' and that 'for petrol cars with catalytic converters, the test may not necessarily identify those cars which will have excessive emissions on the road'.

The NAO's research covered both roadside and MOT emission tests, and the Government watchdog is calling for a standardisation in the way 'engineering discretion' is used at the roadside after finding major discrepancies in failure rates. A host of recommendations for future testing include a review of training in garages to improve standards of testing, backed by incognito garage checks with defective vehicles.