A no-deal Brexit is an existential threat to the British car industry and would risk output, an industry body warned new Prime Minister Boris Johnson on Friday.
Johnson, who took office earlier this week, is ramping up preparations for a potentially disorderly Brexit, although he hopes to achieve a better agreement with the European Union.
The Chief Executive of the Society of Motor Manufacturers and Traders (SMMT) Mike Hawes wrote to Johnson on Friday.
"We are highly integrated with Europe, and a no-deal Brexit would result in huge tariff costs and disruption that would threaten production, as well as further undermining international investors' confidence in the UK," Hawes said in the letter.
"A no-deal Brexit presents an existential threat to our industry."
Several major car companies have warned about the hit they would face to their operations of new tariffs and bureaucracy, which could ruin just-in-time production.
Brexiteers have long argued that Europe's biggest economy, Germany, which exports hundreds of thousands of cars to Britain each year, would do its utmost to protect that trade.