Ralf Speth, CEO of Jaguar Land Rover, repeated his company’s concerns about a possible bad Brexit deal, during a conference in Birmingham, UK.

The boss of Britain’s largest car maker warned that the wrong Brexit deal could cost tens of thousands of jobs in the automotive industry and risk the existence of production facilities, Reuters reports.

Speth said that Jaguar Land Rover would not be able to produce its cars in the UK if post-Brexit custom checks turn the English port of Dover into a “car park” due to delays.

“A thousand (jobs were) lost as a result of diesel policy and those numbers will be counted in the tens of thousands if we do not get the right Brexit deal,” Speth said, referring to redundancies made earlier this year at JLR.

“Currently I do not even know if any of our manufacturing facilities in the UK will be able to function on the 30th (of March),” he added.

JLR’s boss said that unrestricted access to the single market for JLR is “as important a part to our business as wheels are to our cars”.

Jaguar Land Rover, which is about to open a new factory in Slovakia later this year, has already admitted that building cars abroad is cheaper.

“It is thousands of pounds cheaper to produce vehicles for instance in eastern Europe than in Solihull (JLR’s biggest UK plant), and what decisions will I be forced to make if Brexit means not merely that costs go up but that we cannot physically build cars on time and on budget in the UK?” Speth said. “Any friction at our borders puts our production in jeopardy – at a cost of 60 million pounds a day.”

Following the comments of JLR’s boss, a spokesman for British Prime Minister Theresa May said that the government’s Brexit plans include specific proposals to protect jobs in industries dependent on the so-called “just-in-time” supply chains.