 According to MarketWatch on December 7, 2006,

The global foreign exchange market, easily the largest financial market, is dominated by London.More than half of the trades in the derivatives market are handled in London, which straddles the time zones between Asia and the U.S. And the trading rooms in the Square Mile, as the City of London financial district is known, are responsible for almost three-quarters of the trades in the secondary fixed-income markets.In the wake of the 2007-2010 financial crisis, a number of economists and others began to argue that financial services had become too large a sector of the US economy, with no real benefit to society accruing from the activities of increased financialization.