The announcement on Monday that the two top US private securities regulators had completed their merger means there is a new top cop to protect investors: Susan Merrill, the head of enforcement at the new Financial Industry Regulatory Authority (Finra).

Ms Merrill, 50, takes the helm of the combined enforcement arms of the National Association of Securities Dealers (NASD) and the New York Stock Exchange as regulators are struggling to find the right balance between protecting investors aggressively and preserving New York’s ability to compete against countries with laxer regimes. The merger is seen as a way to cut compliance costs and streamline regulation.