British car production fell by a hefty 19.6% in November against last year's pace, according to SMMT data, as export demand slumped (down 23%).
Lower export orders from Europe and Asia combined with the ongoing impact of WLTP alongside planned model and technology changes.
In the year to date, more than 1.4 million cars have been built in the UK overall, an 8.2% year on year decline, with export volumes down 75,085 units and output for the domestic market down 54,143 units.
Mike Hawes, SMMT Chief Executive, said: "It's very concerning to see demand for UK built cars decline in November, with output seriously impacted by falling business and consumer confidence in the UK allied to weakening export markets."
Hawes also issued a warning about the adverse consequences for the UK automotive sector of a 'no-deal' Brexit.
"With fewer than 100 days until the UK leaves the European Union, the automotive industry needs certainty and a 'no-deal' Brexit must be ruled out.
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"Thousands of jobs in British car factories and supply chains depend on free and frictionless trade with the EU – if the country falls off a cliff-edge next March the consequences would be devastating."
Stuart Apperley, Director and Head of UK Automotive at Lloyds Bank Commercial Banking, also highlighted the problems associated with diesel – especially in Europe.
"Today's figures mark the sixth month of falling output," Apperley said.
"The slowdown in China and the USA is adding to the pressure on those firms that manufacture for those or all markets. Meanwhile, ongoing uncertainty about the future of diesel in major markets around the world has put car sales into reverse.
"While nobody can be certain what 2019 might bring, car makers and their supply chains have been planning for all eventualities and an uptick in consumer appetite will be at the top of manufacturers' Christmas wish list."