Lloyd’s of London and other insurers will be forced to move part of their businesses to the European Union if they fail to access the single market following Britain’s decision in June to leave the bloc, Chairman John Nelson said on Monday.

“If we do not get access to the EU single market, what will happen is that business will be written by us and others” in mainland Europe, Nelson said in a BBC Radio 4 interview. “So in a sense, the loser will not necessarily be Lloyd’s or the industry. Sadly, it would be London.”

Underwriters have been making contingency plans, with Lloyd’s saying in February that it had looked at ways of managing the fallout if Britain voted to leave . Shortly before the referendum, Lloyd’s said that such an outcome could put at least 34,000 jobs in the city’s commercial-insurance industry at risk.

Access to the single market and passporting rights is critical to the London insurance market and the wider financial services industry as well as the EU organizations, Nelson said. A prolonged period of uncertainty would force people to act, he said.

“If we do not see a clear direction of travel, we will have to invoke our contingency plans and that would mean moving business or businesses,” he said in the interview.

The EU accounts for about 11 percent of Lloyd’s 25 billion pounds in gross written premiums, according to a spokesman. Lloyd’s won’t relocate its headquarters from London, he said.