Demand for new cars rose by 23.1% last month, figures show.
Some 94,094 new cars were registered in August compared with 76,433 during the same month in 2017, the Society of Motor Manufacturers and Traders (SMMT) said.
The automotive industry body warned that the market is not “booming” and the figures are a result of August being a traditionally slow month for sales.
The introduction of tougher emissions tests from September 1 also led to an increase in sales for certain models, such as the Seat Leon, Honda Jazz and Suzuki Swift.
Overall registrations are down 4.2% this year compared with the first eight months of last year.
Sales of petrol models increased by 39.1% last month, while diesels fell for the 17th consecutive month, down 7.7%.
Demand for alternatively fuelled vehicles such as hybrids and pure electrics increased by 88.7% to take a market share of 8%.
SMMT chief executive Mike Hawes said: “It’s great to see such strong growth, particularly in the important electric vehicle market.
“However, given August is always a small month in new car registrations ahead of the important plate-change month of September, it would be wrong to view the market as booming.
“Indeed, this past month has seen some significant variances as regulatory changes have disrupted some supplies.
“In the long term, however, the new emissions certification test will give consumers renewed confidence in the performance of all vehicles, helping them choose the latest, cleanest technology that best suits their driving needs, whether that be petrol, diesel, hybrid or plug-in.”