Jaguar Land Rover, Britain’s biggest car manufacturer, is to cut production at its Halewood plant as it blamed faltering sales after the Brexit vote and a tax crackdown on diesel vehicles.

JLR said uncertainty around Brexit and the future of diesel cars had weakened demand. Its sales in Britain and Europe were flat in 2017 and the firm said it it expects tough conditions to continue.

In a statement, JLR said it was planning production cuts at the Halewood plant, in Liverpool, which builds three Range Rover models and employs around 6,000 people. JLR said the cuts would take place in the second quarter of 2018.

“Ongoing uncertainty surrounding Brexit is being felt by customers at home and in Europe,” the company said on Monday. “Concern around the future of petrol and diesel engines – and general global economic and political uncertainty – and it’s clear to see why the industry is seeing an impact on car sales.

“Following a review of planned volumes, we are planning to make some temporary adjustments to the production schedule at Halewood in Q2.”

Britain will increase the amount of vehicle excise duty paid by almost everyone buying a new diesel car from April, which will likely hit Jaguar Land Rover. Diesel accounts for around 90% of JLR’s UK sales.

The news came as Vauxhall’s owners, PSA Peugeot Citroën, told trade union leaders that they do not want to close the Ellesmere Port factory, as speculation mounts over the site’s long-term future.

Fears for the future of the Vauxhall factory on the Wirral had been exacerbated after the French owners announced more job cuts earlier this month. Talks took place in Paris on Monday between Carlos Tavares, PSA’s chief executive, and Len McCluskey, the general secretary of Unite.

Unite had warned that PSA sales would be “finished for good” in the UK if Ellesmere Port closed. Vauxhall also makes the Vivaro van at a plant in Luton. Vauxhall employs around 4,500 people at Ellesmere Port and Luton but over the past three months has announced plans to cut 650 jobs in the Wirral.

McCluskey said the meeting was helpful and that PSA had signalled it wanted to keep the plants open. He said: “We had a frank exchange and are now clear on our respective positions.

“Carlos Tavares repeated his desire not to close UK plants, which is reassuring.

“On behalf of Unite, I repeated our determination to safeguard the UK plants and if needs be our willingness to disrupt PSA’s UK market share if the company fails to support this loyal workforce.

“I remain optimistic, however, that we can work constructively with PSA, albeit with the uncertainty and confusion caused by Brexit being a consideration for the company.”

McCluskey said that he would be seeking a meeting with the business secretary, Greg Clark, to press the government to create a more favourable climate for PSA investment. Manufacturers fear Brexit could yet impose higher costs and delays on production.

PSA bought Vauxhall and Opel last year from General Motors. Although PSA pledged to safeguard jobs when the takeover was first announced, in October the new owner announced plans for 400 redundancies at the Wirral plant, which produces the Astra car. Earlier this month, PSA said it would require 250 more jobs to be cut in its recovery plan.