Some investment banks, anxious not to stir speculation of an exodus from the historic City of London and its modern counterpart at Canary Wharf, have given out “business as usual” messages since last week’s shock referendum result. But beyond the soothing words the wider industry is hastily organizing a lobbying effort in the hope London can keep selling financial services across Europe, a right to which it has become accustomed but may lapse when Britain finally exits the 28-nation bloc. The alternative for banks and bankers, growing increasingly insecure in an information vacuum that has developed since the June 23 vote, is to get out. Headhunters report a level of anxious calls they haven’t seen since the 2008 global crisis, with bankers asking about prospects in rival financial centers that remain in the EU, or those in Asia and the United States. Banks and other financial firms have rallied together, forming a group to devise a strategy for protecting the turf of an industry that is Britain’s biggest exporter and accounts for more than 10 percent of its tax revenues.