Every month, some young bureaucrat in the Chinese State Administration of Foreign Exchange (known, slightly menacingly, as SAFE) reaches out to a trader in London and buys or sells billions of dollars’ worth of U.S. Treasury bonds. You’ve heard the overblown fears that China owns too much U.S. debt, but you might not realize that it’s a British firm that regularly gets the commission. That’s because London is the world’s largest market for dollars. When a company in Shanghai or São Paulo decides to sell public shares internationally, they’re very likely to choose London, too.

In fact, if you follow the flow of money around the world, you might be surprised to find that the central node of global finance, the place where money passes through most often, is London, not New York. Wall Street, of course, is no piker. American investment banks — partly because the U.S. economy is the largest in the world — do more business and make more money. But when it comes to international transactions, London is the world’s financial center. The City of London, its Wall Street, employs more than 300,000 people, whereas Wall Street itself employs fewer than 200,000. Banks in the United States hold total assets that come to about 85 percent of the country’s gross domestic product. In Britain, the banks hold almost 400 percent more money than its G.D.P., mainly because so much international business takes place there. And as the U.S. share of global finance shrinks, international business matters more.

How did London surpass Wall Street? In part because even in a world of electronic trading, brokers still want to know there is a human being at the other end of their 0’s and 1’s. London’s working hours overlap with those in the U.S., the Middle East and Asia; New York’s don’t. The more significant reason, however, is regulation. In 1986, Margaret Thatcher instituted what’s known as the Big Bang, which blew up centuries of regulations protecting Britain’s old, slow-moving firms. In an instant, the City of London went from a charming, ancient system of legally protected, relatively small institutions to electronic banking, enormous investment conglomerates and millionaires who made their money via speculative bets. Out were the Oxbridge set and oak-paneled rooms. In were ambitious young men with Cockney accents and walls of Bloomberg terminal screens.

More than any specific change in the law, however, the Big Bang signaled that the government wasn’t going to obstruct people from making oodles of money. And so between 1986 and 2002, this lack of regulation, often called the light touch, helped London catch up with New York. Then, after Congress passed the Sarbanes-Oxley reforms in 2002, the balance of power shifted further. Designed to prevent another Enron, this legislation mandated, among other things, numerous reporting requirements that firms complained were expensive and bureaucratic.