In a move that one industry body called a “cause for concern”, car sales in the UK fell 9% in September.
The Society of Motor Manufacturers and Traders (SMMT) said new car registrations last month numbered 426,170.
From September last year, the figure was down 9.3%.
Meanwhile, diesel sales – which have been hit by worries over air quality – fell by 21.7%.
It was the first time in six years that the key September market had fallen.
Because it marks a change in the licence plate series that indicates how old vehicles are, September is normally a big month for car sales.
Economic and political uncertainty, as well as confusion over air quality plans, had led to a fall in consumer confidence, according to the SMMT.
However, it praised carmakers who were making trade-in and scrappage deals available to UK buyers, saying they were proving popular and should be encouraged.
“September is always a barometer of the health of the UK new car market, so this decline will cause considerable concern,” said SMMT chief executive Mike Hawes.
“Business and political uncertainty is reducing buyer confidence, with consumers and businesses more likely to delay big-ticket purchases.”
The drop in September sales now mean car sales have fallen for the seventh month in a row. The last time there was a decline in September car sales was in 2011, when it fell by a mere 0.8%.
For the year as a whole, sales have reached 2,066,411, representing a fall of 3.9% on the same period last year.
Registrations of new cars have been declining for six months.
Samuel Tombs, chief UK economist at Pantheon Macroeconomics, said, “Car sales remain well below last year’s levels, as the inflation-driven squeeze on real incomes makes households reluctant to make major financial commitments.
“In seasonally-adjusted terms, however, we estimate that registrations were 9.7% higher in [the third quarter] than [the second quarter], when sales were hit by April’s increase in vehicle excise duty.”