Motorists are shunning diesel cars, as they turn to buying vehicles that are much more eco-friendly, industry figures suggest.
The Society of Motor Manufacturers and Traders (SMMT) said that 78,778 diesel cars were sold in January, a drop of 4.3% on the same month last year.
Over the same period sales of electric cars and other alternatively-fuelled vehicles (AFVs) jumped by 19.9%.
For the first time, AFVs now account for more than 4% of the market.
The figures show that 7,270 AFVs – including hybrids – were sold in January, gaining a 4.2% market share.
Sales of diesel cars have been falling for several months, following publicity about pollution and health issues.
In December 2016, sales of diesel cars were down by 6.8% on the same month a year earlier.
Several big cities around the world have said they want to ban diesel cars within 10 years, because of the pollution they cause.
A group of doctors has called on the Mayor of London to ban them in the capital, while Westminster will hit some diesel drivers with extra parking charges from April.
The government is also thought to be planning a diesel scrappage scheme, to encourage motorists to ditch cars which are the heaviest polluters.
However, the SMMT figures show that overall sales of vehicles in the UK last month were at their highest January level in 12 years.
In total 174,564 cars were sold, a rise of 2.9% on January 2016.
Motorists who buy electric or hybrid petrol/electric cars still enjoy a grant from the government, worth up to 35% – or £4,500 – of the total value.