The UK-based Fleet Alliance says that confused government policy towards diesel vehicles, which has led to falling sales of cars powered by the fuel, has caused the first ever increase in average CO2 emissions across its fleet.

The leasing and fleet management company says average emissions from its 28,000 vehicles increased from 115g/km in 2017 to 125g/km in 2018, a rise of almost 9%.

It says that although the increases were biggest among its personal contract hire customers, average emissions among business contract hire customers still rose from 114g/km to 117g/km.

The firm says it saw orders for diesel cars from fleets fall from 73.35% to 66.6%, while petrol orders rose from 16.96% to 21.65%.

The remainder was accounted for by alternative fuels – 7.81% by plug-in hybrids, 3.59% by conventional hybrids and only 0.27% by pure electric cars.

Fleet Alliance says the rising CO2 levels are in line with UK trends reported by the Society of Motor Manufacturers and Traders (SMMT) and European trends reported by Jato Dynamics.

Fleet Alliance managing director Martin Brown said: "What we are seeing first hand is a direct result of misguided government policy and an anti-diesel stance which is completely unjustified."

"It is almost unthinkable that we should see CO2 emissions increase on a national level after all the hard work undertaken in bringing them down over the last 20 years. 

"But the figures from our own fleet back up the findings by the SMMT and JATO – namely that CO2 levels are on the rise, and it is largely attributable to the government's punitive anti-diesel stance and a lack of joined up thinking on national transport policy."