The Society of Motor Manufacturers and Traders (SMMT) said 136,119 new cars were built in May, 9.7% fewer than the same month in 2016.
However, in May 2016 output had risen by more than 26% to the highest total for the month in more than a decade.
The SMMT said carmakers were now set to ramp up production of new models, with exports the main driver of demand.
Some 576,556 new cars have been shipped abroad since January, a 0.8% increase year-on-year. although production for overseas markets fell 9% in May.
Almost 80% of all cars made in Britain are exported, with more than half going to Europe.
Meanwhile, production for the home market fell 12.8% in May, with 153,199 cars destined for UK showrooms.
"After a record start to the year, car production in the UK has slowed as production lines gear up for a range of new models," said SMMT chief executive Mike Hawes.
"Global demand is strong and exports remain the driving force for British car production volumes in the UK.
"Maintaining our current open trade links with Europe, our biggest market, and further developing global markets is vital for this sector."
Production of new UK cars fell by almost 10% last month compared with a year ago, latest industry figures show.