The CEO of insurance company RSA (LON:RSA) has spoken out against a British exit from the European Union, warning that it could have a negative impact on business and investment returns.

After his comments, Stephen Hester became the latest in a string of influential figures in British business is highlight concerns over the impact of a Brexit, and was one of 36 CEOs of FTSE 100 companies to sign an open letter arguing that leaving the EU would put the UK’s economy at risk.

“Half of our market value comes from our European businesses, and in all of our markets, some of our major competitors are European,” Hester told Reuters. “A level playing field between European competitors and ourselves is valuable to us in the long run.”

If a Brexit does impact on business, RSA has a lot to lose – its most recent set of results, released on Thursday, saw a 43 percent rise in operating profit to £523 million, sending shares up over 10 percent. Underwriting profit was up by 437 percent, with the final dividend up 250 percent. Hester took on the job as CEO two years ago with the intention of turning the company around, after an aborted takeover by Swiss insurance giant Zurich.

Hester said: “2015 was a year of major achievement for RSA. As a result, the turnaround phase of our Action Plan is largely complete and we have good prospects of substantial further performance improvement.”

Shares are currently up 12.85 percent at 445.20 (1257GMT).

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