The Society of Motor Manufacturers and Traders says only 347 million pounds ($460 million) is being invested in new models and facilities during the first half of 2018 compared to 647 million pounds used that way during the same period the year before.
On June 21, the House of Lords of the UK Parliament approved the EU Withdrawal Bill.
"Our message to government is that until it can demonstrate exactly how a new model for customs and trade with the European Union can replicate the benefits we now enjoy".
The UK vehicle industry is suffering from the ongoing uncertainty around Brexit, it was confirmed today. "The current position, with conflicting messages and red lines goes directly against the interests of the United Kingdom automotive sector which has thrived on single market and customs union membership".
Earlier this week, German carmaker BMW - which employs nearly 8,000 people and has four plants in the United Kingdom - warned it can not manufacture its products in the United Kingdom if Brexit means its supply chain is disrupted.
But senior director Stephan Freismuth said delays in importing components would put the operation under serious threat, potentially forcing United Kingdom closures.
"The UK government and the European Union will need to agree on all aspects of regulatory alignment, which is of the utmost importance, without jeopardising the integrity of the single market", they added.
"It would be foolhardy of any company not to have these contingency ideas under way because we are racing towards March 29 next year". "Don't change it", he said.
In an open letter to British Prime Minister Theresa May, 60 lawmakers, economists and business chiefs have accused the European Union of being "intransigent" in divorce talks and said Britain should threaten to withhold the 39 billion pound ($52 billion) divorce bill it has already agreed to pay.
In the interests of both boardrooms and ordinary workers, the two sides' actions must seek to preserve value chains and avoid non-tariff trade barriers, find solutions for barrier-free and frictionless trade in goods and services and a mechanism to agree a level playing field for workers' rights, the statement said.
Animosity between the European Union and the United Kingdom has slowed Brexit negotiations, and there is an increasing risk that the United Kingdom and European Union will not reach an effective agreement on future trade relations by the time Britain officially leaves in March next year.
Airbus employs 14,000 people at 25 sites across the country.