Many motorists switched from petrol to diesel vehicle after tax changes were introduced by Tony Blair and Gordon Brown

Tony Blair’s government ignored health warnings over air pollution as it pushed ahead with tax changes that led to a fourfold increase in the number of diesel vehicles on Britain’s roads, confidential Treasury files released yesterday show.

Ministers were aware that an influx of diesels would damage air quality and were advised that a new levy would be required so as not to incentivise their purchase over petrol cars. However, officials working on the 2000 budget dismissed the warnings for presentational reasons, amid fears that the government would be seen as “overly harsh on diesel users”.

Gordon Brown, the chancellor, went on to introduce a sliding scale for vehicle excise duty, with lower rates for cars with lower carbon dioxide emissions. Many motorists switched from