Will Brexit Trigger Exodus of Banks From London?:London has flourished as a financial center for decades in part because global banks, from offices around the bustling City of London district, could sell their services freely around the European Union’s 28-nation trading bloc. Now that British voters have decided to leave the EU — the complicated international divorce known as Brexit — the city’s status as a banking hub is under threat. If U.K. firms lose easy access to Europe’s $19 trillion eco…