All new diesel-engined cars fall below EU standards for NOx emissions according to real-world driving tests conducted by the International Council of Clean Transportation (ICCT), the organisation which first brought the Volkswagen scandal to light.

ICCT found four manufacturer groups with average vehicle emissions over 12 times higher than the Euro 6 diesel limit, with the worst offending vehicle family emitting 18 times the limit.

The dataset comprises samples from emissions tests for over 700,000 cars and 4,850 models – of Euro standards 3-6 – across France, Spain, Sweden, Switzerland and the United Kingdom.

The real-world sampling method used is 'difficult to impossible' to cheat according to the ICCT, involving passing a beam of light through the exhaust emissions of a car from a sampling location on the road. Automatic plate recognition technology is then used to determine the model of car being recorded.

This remote sensing technology was used to measure emissions of over 100,000 vehicles in London during a five-month sampling campaign between late 2017 and early 2018.

Rankings are divided into three tiers: green for vehicles with less than 90 milligrams of NOx per kilometre, yellow for 90-180mg/km, and red in excess of 180mg/km.

No Euro 6 standard diesel engine achieved a green rating. Only BMW's range of diesel cars achieved a yellow rating. Euro 5 diesel families showed particularly poor rankings, with NOx emissions at least twice the limit.

Petrol cars were better ranked, receiving 'good' or 'moderate' ratings, with the highest-emitting petrol Euro 6 vehicle reaching similar levels of NOx emissions to the lowest-emitting diesel vehicles.

All results have been entered into a searchable database by the Real Urban Emissions Initiative (True), with the aim of providing greater transparency around urban air quality.

Nick Molden, chief executive of Emissions Analytics, cautioned that – despite being a "brilliant" screening tool" – the True rating does not account for when later models have cut emissions significantly, citing improvements made between 2014 and 2017 Mercedes-Benz models.