British support for leaving the EU has risen, with the Out campaign now having a 4-5 percentage point lead, according to opinion polls published on Monday.

Robertson, who was born in western England and brought up in Wales, fears that Britons do not fully grasp what is at stake in the referendum on June 23.

“The U.K. is a prosperous economy but if you imagine it without the flow of labor from the EU, I firmly believe that the British economy would not be in as strong a shape as it is,” Robertson, 58, said in an interview at BMW’s headquarters in Munich, southern Germany.

The global car and motorbike group, with its roots in Bavaria, owns the BMW (BMW-HM), Mini, and Rolls-Royce brands and employs 122,700 staff.

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Around 7,800 of its employees work in factories dotted around Britain, including those producing Mini and Rolls-Royce cars, two brands that use their British heritage to market themselves around the globe.

Underscoring the point, Prime Minister David Cameron, campaigning to keep Britain in the EU, appeared on Monday in front of a row of Minis with the message “Stronger In” on their license plates.

An exit would make Britain less attractive as a location for investment even though demand for premium cars is solid, Robertson said.

“The U.K. is BMW’s fourth-largest market. The customer strength on the ground means that the investment case for the U.K. is there anyway. But part of the attraction is that ability to export as well as to import, and to do it in the most logistically friendly way.”

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Much of the British car industry is now in foreign hands and Robertson argues that access to markets across the 28-nation EU played a crucial role in attracting overseas investment.

“If you look at the investment into the U.K. auto sector that occurred—whether it was from Germans, Americans, Japanese, or latterly Indians—the ability to be part of the EU was a factor when those decisions were made,” Robertson said. “It wasn’t the only factor, but it was an important one.”

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Businesses ranging from budget airline Ryanair to U.S. bank J.P. Morgan Chase (JPYYL) have warned of the economic consequences should Britain vote to leave.

Robertson, who headed BMW’s South Africa business from 1999-2005, is cautious about whether Mini might make changes to its production network in the event of an exit vote.

“At the end of the day, the British people are going to make a decision, and then we will consider what the next steps are,” Robertson said. It is less critical because BMW broadened its manufacturing footprint even before the Brexit debate started, as part of a “produce where you sell” strategy.

Today the Mini, for example, is made in Austria and the Netherlands as well as in England. BMWs are produced in China and the United States as well as Germany.