"We believe that London will continue to be an important financial centre, although maybe not as important as it is today," Ermotti told the news agency, adding "we are well prepared for any outcome".

UBS employs more than 5,000 people in London. Ermotti said that 20 percent to 30 percent of those employees could be affected should the Swiss bank decide to move.

UBS now passes on the cost of negative interest rates to its institutional customers. So far, it has not followed suit for retail clients, he said, but it is not ruling out such a move.

"Charging negative rates, in a deflationary environment, isn't something that clients would accept easily," he said. "If we did, it would be better to hold your cash in a safe."

(Reporting by Josh Franklin, writing by John Miller)