Almost a third of all government car service vehicles procured since 2015 were diesel, despite them being primarily operated in central London, where air quality is a major issue.
Air pollution is linked to 40,000 early deaths in the UK from lung and heart disease, as well as being linked to other health conditions, with diesel cars a major source of toxic nitrogen oxides.
This is one of a string of failures the Government racked up recently in its ambition to move the UK to low emission electric vehicles.
Shortly after prime minister Theresa May made tackling climate change a key part of her legacy, it was revealed that her government has been dragging its heels in making the switch to electric vehicles, something chancellor Philip Hammond put front and centre in his 2017 budget.
Transport minister Michael Ellis revealed in a parliamentary answer that the Government Car Service (GCS) has procured 65 vehicles since July 2015 and 20 of these were diesel.
At the Department for Transport (DfT) electric vehicles make up just 23% of the entire fleet.
Central government cars are not due to go electric for another 11 years, and only 25% of the fleet will be electric by 2022.
Transport secretary Chris Grayling has written to every Government department to reinforce the pledge to move towards a completely electric Government fleet by 2030.
Transport Network can also reveal that the Department for Transport (DfT) has failed to enact key aspects of the Automated and Electric Vehicles Act, which would force major fuel suppliers to provide electric vehicle charging.
Despite the Act being passed just over a year ago, the DfT appears to have made no effort to make use of the powers.
When the legislation was passed last July, the DfT boasted that the Act 'will see a massive improvement in electric chargepoint availability; giving the government new powers to ensure motorway services are upgraded with plenty of points, and even allowing mayors to request installations at large fuel retailers in their areas'.
It went on to say: 'The new laws will improve consumer confidence in charging their vehicles by making sure that public chargepoints are compatible with all vehicles standardising how they are paid for setting standards for reliability.'
However, the transport secretary has not imposed the regulatory powers under the Act to enforce the provision of charging points or allow directly elected 'metro mayors' to do so, meaning the legislation is effectively meaningless in this area.
When questioned by Transport Network, a DfT spokesperson said the Government continues to monitor market developments closely, and keeps the possibility of using powers provided the Automated and Electric Vehicles Act under constant review - including what officials called the consideration of whether to regulate to allow metro Mayors to require chargepoints at large fuel retailers.
The spokesperson said: 'Nearly 120,000 chargepoints have been installed across the UK to date. We are continuing to accelerate the growth of electric vehicle infrastructure through a range of initiatives, including up to £500 off the upfront cost of residential installations.
'The Government has also established a £400m public-private Charging Infrastructure Investment Fund, as part of its £1.5bn programme to transition to zero emission vehicles.'