Jaguar Land Rover has announced a cut in production due to “continuing headwinds” affecting the car industry, hours after its chief executive was accused of fabricating warnings about potential hard Brexit job losses.

The automotive giant said it was making “temporary adjustments” at its Castle Bromwich site in Birmingham, with the area’s MP saying staff had been placed on a three-day week until Christmas.

The move came hours after former shadow minister Sir Bernard Jenkin accused Professor Dr Ralf Speth of scaremongering over a prediction that crashing out of the EU would have a “horrifying” effect on the leading automotive firm’s business.

Prof Speth had told the UK’s first Zero Emission Vehicle Summit in Birmingham last week – attended by the Prime Minister – that a hard Brexit could result in the “worst of times” for the UK while the cost to Jaguar Land Rover would be more than £1.2 billion a year.

Asked his view on the German businessman’s warning on Monday, Sir Bernard, a member of the Eurosceptic European Research Group, told BBC Radio 4’s Today: “I’m afraid I think he’s making it up.

“We’ve had figures made up all the time by the scaremongers in this debate and I’m afraid nobody believes them.”

The comments sparked criticism from Labour and from within the Harwich and North Essex MP’s own party.

In a tweet, Labour’s Jack Dromey said that Castle Bromwich, which is in his Birmingham Erdington constituency, was moving onto a three-day week until Christmas due to a combination of “Brexit chaos” and the “mishandling by ministers of the transition from diesel”.

He described Prof Speth as “the man … who has transformed (Jaguar Land Rover) into a world-class success story, doubling the company in size to over 40,000”, adding: “The irrational zeal of the #Brexiteers is breathtaking!”

The warning by Prof Speth – who has worked in the car industry for more than 30 years – followed similar warnings from other industry bosses, including Airbus and BMW, about the potentially damaging consequences of Britain’s decision to leave the EU.

Sir Bernard’s comments were described as “embarrassing” by pro-Remain Tory MP Anna Soubry.

She said on Twitter: “The Conservative Party is the party of business. I’m backing Raif (sic) Speth & all the other business leaders & trade unions who are being honest about the disaster of a #NoDeal hard #Brexit & are increasingly backing @peoplesvote_uk.”

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Ralf Speth, chief executive officer of Jaguar Land Rover, had warned about the impact of a hard Brexit (Chris Ratcliffe/PA)

Jaguar Land Rover declined to comment on sir Bernard’s comments.

In a statement regarding Castle Bromwich, it said: “As is standard business practice, Jaguar Land Rover regularly reviews its production schedules to ensure market demand is balanced globally.

“In light of the continuing headwinds impacting the car industry, we are making some temporary adjustments to our production schedules at Castle Bromwich.

“We are, however, continuing to over-proportionally invest in new products and technologies, and are committed to our UK plants, in which we have invested more than £4 billion since 2010 to future proof manufacturing technologies to deliver new models.”

Unite assistant general secretary Tony Burke said: “This is the continuing effect of the chaotic mismanagement of the Brexit negotiations by the Government which has created uncertainty across the UK’s automotive industry and the manufacturing sector generally.

“It is also the result of the mishandling of how the UK makes a just transition from diesel and combustion engines to electric vehicles. Both issues have damaged the ‘jewel in the crown’ of UK manufacturing – our automotive industry.

“The situation is not helped when you have arch-Brexiteer MP Sir Bernard Jenkin accusing Ralf Speth of ‘making it up’ when it comes to Brexit and the car industry.

“Jenkins’ comments are highly irresponsible and misinformed when future employment is at stake and are entering into the world of fantasy economics.”