Diesel car pollution is 25 times over legal limit

New diesel cars are up to more than 25 times over the legal pollution limit, a new study into manufacturer emissions tests has revealed.

The International Council on Clean Transportation (ICCT) found the average car produces seven times more nitrogen oxides than the Euro 6 standard which came into effect last month.

Just one of the 15 cars that were tested met the 60mg per kilometre target with the worst result hitting a staggering 2,000mg per km.

• Diesels causing illegal air pollution across the UK

Dangerous levels of nitrogen oxides have been linked to thousands of premature deaths in the UK and the increasing popularity of diesel cars has been a huge factor. It's led London Mayor Boris Johnson to float the idea of charging diesel drivers an extra congestion charge.

The British pollution tests, carried out by Emissions Analytics, revealed the Mercedes C200 and Citroen C4 Cactus produced three times the limit - but it said it could not release the whole data for all the tests.

The tests were conducted in real-world conditions and included quick bursts of acceleration and longer periods travelling at 60mph. That's quite different to the official tests which are conducted in a controlled laboratory with smooth and gentle acceleration. The ICCT said the results that broke the limit were recorded during normal driving and not at extreme moments. 

• £11million investment in hydrogen fuel

Vicente Franco, an ICCT researcher and study author, said the results proved some manufacturers were developing the right technology but it wasn't necessarily being used correctly. Selective catalytic reduction tech, for example, is calibrated by manufacturers to work at its peak during the official tests rather than in real world driving.