The first half of the year was the best since 2008, with three cars built in the UK every minute, but July saw a slowdown, said the Society of Motor Manufacturers & Traders (SMMT).
There were 117,665 cars manufactured last month, an 11.2 per cent drop on the same period last year.
The fall is likely to be down to some firms pausing production in the summer period and workers taking holidays, said SMMT chief executive Mike Hawes.
He said: “Car production is traditionally subject to a degree of fluctuation during the quieter summer months with some manufacturers pausing production to invest in upgrades and prepare for new model launches, as well as to manage holiday leave.
“The industry remains in a strong position, with more than 911,000 cars produced so far this year and some significant introductions due in the autumn.”
So far this year 911,307 cars have been built, down 1.4 per cent on the same period last year. Domestic demand rose 8 per cent, while exports fell 3.9 per cent.