The number of cars produced in the UK fell by 45% in April as factories closed to cope with anticipated Brexit disruption.
Factories across the UK planned shutdowns due to the initial 29 March Brexit deadline, and went ahead with them despite the delay to Brexit.
Car factories have annual shutdowns but usually take place in summer. They brought them forward in order to stockpile materials and train staff on customs procedures.
Car manufacturers have said they will not be able to hold another shutdown ahead of the new Brexit deadline of 31 October.
The Society of Motor Manufacturers and Traders (SMMT) said 71,000 cars were built in April in what it describes as an "extraordinary month". That was a 57,000 drop compared with April last year.
Mike Hawes, SMMT chief executive, said: "Today's figures are evidence of the vast cost and upheaval Brexit uncertainty has already wrought on UK automotive manufacturing businesses and workers.
"Prolonged instability has done untold damage, with the fear of 'no deal' holding back progress, causing investment to stall, jobs to be lost and undermining our global reputation."
April was also the 11th consecutive month in which output has fallen in the UK. In the year to date, production is down by 20% compared with the same period last year. It is ahead of the SMMT's estimates that output would drop 10% in 2019. Last year the SMMT said a good deal with the EU would allow production to pick up again towards the end of the year, but the threat of a no deal could lead to bigger falls.