Published: 1:48 PM September 11, 2018 Updated: 6:18 PM September 17, 2020

The boss of Britain's biggest car manufacturer, Jaguar Land Rover, has launched a blistering attack on Brexit plans, warning that 'tens of thousands' of jobs in the car industry could be lost if the UK crashes out without a deal.

Ralf Speth, the company's chief executive, said he was concerned delays in the supply chain could halt production and repeated warnings that a Hard Brexit could cost £1.2bn.

Dr Speth said that, as his firm produced 3,000 cars daily and relied heavily on "just in time" supply chains where parts are delivered shortly before they are used, he would be "very, very concerned" if there were blockages in the supply of parts.

He told Sky News: "Just one part missing could mean stopping production at a cost of £60m a day.

"That is a huge risk. We depend on free, frictionless, seamless logistics."

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Dr Speth also repeated his warning, made in early July, that a Hard Brexit would cost Jaguar Land Rover, the biggest private sector employer in the West Midlands, £1.2bn.

He was speaking at the Zero Emission Vehicle Summit in Birmingham, attended by the prime minister and other members of the cabinet.

In comments made moments before May took to the stage herself, Dr Speth also said Jaguar Land Rover would not be able to continue making cars if the motorways to and from Dover became a car park.

He said that it was cheaper to make cars in Slovakia than it currently was in Britain, adding: 'What decisions will we 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?'.

He warned: 'Six months from Brexit and uncertainty means that many companies are being forced to make decisions about their businesses that will not be reversed, whatever the outcome, just to survive.'

The firm is already moving production of its Discovery model from the UK to Slovakia early next year, which is likely to affect hundreds of jobs.

Labour MP Madeleine Moon, a champion of the anti-Brexit campaign group Best for Britain, said Dr Speth's warnings were "truly shocking news".

She said: "The automotive industry has been warning of the dangers facing their sector for a while and now we're it looks like we're on the road to automotive disaster.

"Jobs have already gone in a number of car factories because of Brexit. Now we are facing the death of the jewel in the crown of UK manufacturing.

"When will this government finally admit to the damage they're causing and start to listen to groups like the Society of Motor Manufacturers and Traders who don't want British cars stagnating in the slow lane?".