For Mr. Magal, the threat of trade tariffs is forcing him to rethink the structure of his business. The company assembles thermostatic control units for car manufacturers, including Jaguar Land Rover in Britain and Daimler in Germany.

Tariffs could add anything up to 10 percent to the price of some of his products, an increase he can neither afford to absorb nor pass on. “We don’t make 10 percent profit — that’s for sure,” he said, adding, “We won’t be able to increase the price, because the customer will say, ‘We will buy from the competition.’ ”

The logic is to reduce the amount of products that are made in Britain for continental Europe, and vice versa. Mr. Magal said that European clients were asking him to consider moving production.

“With all the new projects we are getting now from Europe, they are saying, ‘Why can’t you put it in your plant in Europe? Why do you need to do it in the U.K.?’ ” he said.

If there is a hard Brexit, as seems increasingly likely, some production might be shifted to Britain from the Continent to serve the British market, but more would shift the other way, Mr. Magal said, adding that some parts could be made only in Germany.

It is unclear what the impact will be on the Reading factory and its 230 jobs, or on another British factory that employs about 100 people.