Banks in the U.K. will start relocating operations out of the country by year-end, months before formal talks to leave the European Union begin, as London looks set to lose access to the EU single market, the head of the British Bankers Association said in a newspaper commentary.

International banks' “hands are quivering over the relocate button,” Anthony Browne, chief executive officer of the banking lobby group the BBA, wrote Sunday in the Observer newspaper. “Many smaller banks plan to start relocations before Christmas; bigger banks are expected to start in the first quarter of next year.”

Without identifying any banks by name, he said lenders can't wait until the last minute and have to “plan for the worst,” especially because “public and political debate at the moment is taking us in the wrong direction.”