“This will be the most consequential thing post-war we’ve ever seen,” Mr Kelleher said yesterday in an interview on Bloomberg Television.
“Initially, the fall-out can be controlled, but the political ramifications are actually quite profound,” he said.
Financial markets have been on edge ahead of today’s UK referendum on EU membership. The latest polls show the outcome is too close to call, though betting shops on Tuesday put the probability of a vote to leave the EU at about 26%. The uncertainty comes as investors are grappling with continued signs that global growth remains tepid.
“We’re hoping the British voter will show sense and listen to the economic arguments and stay,” Mr. Kelleher said. “But we clearly are looking at our plans,” he said, adding the New York-based firm would consider moving its European headquarters from London.
Mr. Kelleher, 59, has run the firm’s investment bank and trading division since 2013 and gained oversight of the brokerage in January when he was promoted to president. He’s worked at Morgan Stanley or predecessor firms for more than 25 years.
A so-called Brexit would cost a material number of UK finance positions as things like the clearing of the euro currency would shift to the continent, he said, adding that over the longer term, there would be issues related to visas and the movement of labour.
“London cannot suffer in the event of a Brexit vote, and the reason for that is historic,” Mr Kelleher said. “London has done very well by virtue of being part of the European Union. Its market, the exchanges, clearing, everything is based in London.”
Even if the UK opts to remain, markets are unlikely to climb significantly or return to higher trading volumes because of prolonged low-interest rates and growth, he said. When asked if the US election also affected markets, Mr Kelleher cited oil and China as reasons for investor indecision.
“What we have seen generally is a big fall-off in client volumes, and you’re seeing that because of a lot of uncertainties,” he said. “It’s a number of things causing people to be nervous. And we have seen a fall-off, a significant fall-off, and some could argue even a secular change because of the changes.”
The EU’s financial services commissioner also said, yesterday, banks could be forced to relocate jobs from London to Frankfurt and Paris if the UK voted to leave the EU.