Sales of new cars fell 8.5% in May from a year earlier, with buyers cautious in the run-up to the general election, the Society of Motor Manufacturers and Traders (SMMT) has said.
The SMMT said 186,265 new cars were registered in May.
But sales of alternatively fuelled cars rebounded after falling in April. They now have a record 4.4% market share.
More than 1.1 million new cars have been registered this year to date, down 0.6% on 2016.
"Although demand has fallen, it's important to remember that the market remains at a very high level and with a rate of new models packed with the latest low-emission and connected technology coming to market this summer, we expect the market to remain strong over the year," said SMMT chief executive Mike Hawes.
Car sales in April and May have suffered after a record 562,337 new vehicles were registered in March, as buyers rushed to beat a rise in Vehicle Excise Duty (VED) that came into force on 1 April.
"We expected demand in the new car market to remain negative in May due to the pull-forward to March," Mr Hawes said.
"Added to this, the general election was always likely to give many pause for thought and affect purchasing patterns in the short term."
More than half of all cars sold in May - 96,518 - were petrol-driven, slightly up on May 2016.
Diesel accounted for 81,489 sales, 20% fewer than a year earlier. Alternatively fuelled vehicles went up 46.7% to 8,258.