The new car market has declined for a fourth consecutive month, industry figures show.
Just under 162,000 new cars were registered in July, down 9.3% on the same month last year, according to the Society of Motor Manufacturers and Traders (SMMT).
Some 1.56 million new cars have been sold so far this year, a decrease of 2.2% on the same period in 2016.
The SMMT said the market is continuing to fall amid growing uncertainty over Brexit and is in line with forecasts.
SMMT chief executive Mike Hawes said: "The fall in consumer and business confidence is having a knock-on effect on demand in the new car market and Government must act quickly to provide concrete plans regarding Brexit."
Registrations of new diesel cars fell 20.1% in July, with petrol models down 3%. Alternatively fuelled vehicles rose 64.9% and achieved a record market share of 5.5%.
Ministers last week announced proposals to ban the sale of all conventional diesel and petrol cars by 2040 as part of their court-mandated plans for meeting legal European Union limits on harmful nitrogen dioxide pollution.
They are also considering funding measures to cut pollution with a tax on new diesel vehicles.
Mr Hawes said: "While it's encouraging to see record achievements for alternatively fuelled vehicles, consumers considering other fuel types will have undoubtedly been affected by the uncertainty surrounding the Government's clean air plans.
"It is important to remember that there are no plans to charge drivers using the latest Euro 6 models and no proposed bans for conventional petrol and diesel vehicles for some 23 years.
"The lower demand in recent months will inevitably mean competition from manufacturers will intensify and it will be a good opportunity for consumers to get a great deal on their next car, with many exciting new models launched in the coming months."