UK new-car registrations fell 4.1 percent to 161,064 in April, dragged down by weak demand from consumers worried about the future of diesel vehicles and the consequences of Brexit, according to data from the Society of Motor Manufacturers and Traders (SMMT).
Sales to private motorists fell by 10 percent, while fleet sales rose 2.9 percent.
Sales of diesel vehicles fell 9.4 percent, giving the powertrain a 28.9 percent market share, while gasoline was down 3 percent to a 64.7 percent share.
Alternative-fueled vehicles, such as electrified vehicles, increased 13 percent for a 6.4 percent market share. However, plug-in hybrid sales were down 34 percent, which the SMMT said demonstrated the consequences of removing purchase incentives for the technology before the market is ready.
"We need policies that help get the latest, cleanest vehicles on the road more quickly and support market transition for all drivers. This includes investment in infrastructure and long-term incentives to make new technologies as affordable as possible," the association's CEO Mike Hawes said on Tuesday in a statement.
Top-selling brands had a mixed month. Sales at market leader Ford fell 10 percent, while No. 2-ranked Volkswagen gained 3.7 percent. No. 3 Audi saw volume drop 5.1 percent, ahead of rival Mercedes-Benz at No. 4, whose sales dropped 0.9 percent. BMW rounded out the top five sellers with sales up 20 percent.
- Download file here for UK sales for April, 4 months
Among other brands, sales at Renault plunged 27 percent, Nissan fell 15 percent, Fiat was down 13 percent and Vauxhall's volume dropped 5.1 percent.
Land Rover and Jaguar had a good month with sales gains of 13 percent and 8 percent respectively.
Through April, UK sales were down 2.7 percent to 886,400.
Reuters contributed to this report