If Britain leaves the European market, it will lose the benefits of the bloc’s trade deals. In short, just as Japan and Europe are liberalizing trade with each other, Britain is moving to impede trade with both.

“The big worry is investment,” said Mike Hawes, chief executive of the Society of Motor Manufacturers and Traders, an industry trade group. “Investors are just waiting to see, is it worth continuing to commit to the U.K. automotive industry?”

The British economy is now 1 to 2.5 percent smaller than it would have been without the Brexit vote, economists estimate. Much of the damage has come via the drop in the British pound, which has shed more than 10 percent of its value against the dollar since the referendum.

The fall in the pound amounts to the market’s expression that trade has been obstructed. Britain sells nearly half of its exports within the European Union.

Given that Britain imports more than it exports, the falling currency has pushed up prices on a broad range of goods, from fruits and vegetables to machinery. Inflation was the primary factor in median household income’s remaining flat last year, according to an analysis by the Institute for Fiscal Studies, an independent research firm in London.

Across Britain, business investment is expected to decline by 1 percent this year, in what would be the weakest performance since the global financial crisis a decade ago, according to a recent forecast from the British Chambers of Commerce.