William Donaldson, chairman of the US Securities and Exchange Commission has warned that public confidence in financial markets and exchanges must not be damaged by efforts to overhaul them and said investors must have access to the best price for their orders.

Speaking at a hearing on the SEC's proposed regulation NMS, which is designed to enhance the structure of US equity markets, Donaldson said: "It is very hard to see how, if there's an accessible price that's a better price and if that price is bypassed, that that isn't something that's not in the public interest. It's hard for me to conceive."