According to Department for Transport figures, the number of diesel cars licensed in Great Britain has risen from 12 million at the end of 2016, to 12.4 million at the end of last year.
The number of diesel on the road has almost doubled from 6.6 million in 2007.
The figures also show that of 31.2 million cars in Great Britain at the end of 2017, 18.3 million were powered by petrol, 414,000 were hybrid electric and 45,000 were pure electric.
In addition, the number of vans – almost all of which will be powered by diesel – is also at a new high with 3.9 million in Britain.
Steve Gooding, director of the RAC Foundation, said: “These latest figures show just how entrenched diesel cars are in our society. It also illustrates that even if the dramatic drop in sales of new diesel cars continues it will take several years before the size of the overall diesel fleet is significantly dented.
“It’s not just diesel cars that are at record numbers. The van fleet has just hit a new high of 3.9 million and almost all of these will be powered by diesel.
“The new figures also show that the average age of cars in Britain now stands at 8.1 years. This is up from eight years in 2016 and 6.8 years a decade ago.”