Some diesel vans are exceeding their emissions limits by more than 12 times, according to on-road tests carried out by Emissions Analytics.

The research, which is likely to give further ammunition to the anti-diesel lobby, found Euro6 models such as the Mercedes-Benz Citan, the Peugeot Boxer, the Fiat Professional Doblo and the Vauxhall Combo emit at least 12 times the NOx (nitrogen oxide) permitted under the Euro6 standard.

Emissions Analytics’ Equa Air Quality Index also listed Ford’s Euro6 models the Transit Connect light van and the Ranger pick-up truck as emitting up to eight times the Euro6 NOx limit.

The 2.0-litre Euro6 Transit Custom medium van fared better – the index found it met Euro5 standards – but of the 25 Euro5 and Euro6 LCVs tested (nine Euro6, 16 Euro5) the 2.0-litre Euro6 VW Transporter was the cleanest vehicle in terms of NOx emissions, almost hitting the 80mg/km nitrogen oxide regulation – indicating that the manufacturer has cleaned up its act since becoming embroiled in an emissions-rigging scandal in September 2015.

Nick Molden, Emissions Analytics’ CEO, told What Van?: “Van traffic and deliveries are causing a growing proportion of urban nitrogen oxide emissions, putting out even more pollution on average than diesel cars. Yet there are big differences between the cleanest and dirtiest, and it is the Equa Index that allows you to find those good performers.”

None of the LCVs Emissions Analytics tested under “real-world conditions on the road” matched the official mpg figures given by their manufacturers. Emissions Analytics said the laboratory-based New European Drive Cycle (NEDC) test used to measure emissions is not fit for purpose as a real-world guide – particularly for vans because it does not take account of the affect payload has on fuel consumption. In September 2017, the World Harmonised Light Duty Test Protocol (WLTP) will replace the NEDC.

Emissions Analytics said: “The WLTP drive cycle contains higher speeds and accelerations than the NEDC, better reflecting real driving. However, the test remains entirely in the laboratory.” It added the WLTP remained susceptible to manufacturers optimising their vehicles for the test and claimed that while it represented an improvement on the current system, it would only “partially close the gap between official data and reality”.

The organisation claimed it has designed an on-road test that includes a mix of road types, speeds and gradients, which also takes climate conditions into consideration. Using a portable emissions measurement system (PEMS) it measures what comes out of the exhaust pipe with an on-board gas analyser, and for LCVs a payload of 125kg plus driver and passenger is included.