Governments of the world's biggest economies have applied moral pressure for more than a decade on Switzerland, Liechtenstein, Luxembourg, Singapore, Monaco, and a host of countries that allow the well-heeled to park their money out of the sight of tax authorities at home.
Now, they are threatening to replace the tough talk with strict sanctions on those countries that continue to shelter tax evaders with bank secrecy rules. One by one, the tax havens are caving in.
"We have made more progress in the past 13 days than in the last 13 years," says Jeffrey Owens, head of the tax policy unit of the Organization for Economic Cooperation and Development (OECD), a group of 30 democracies that is seeking to establish a global standard for tax cooperation.
In London, G-20 leaders are expected to push for those countries that refuse to sign up to the OECD tax agreement to be put on a black list and face possible sanctions, including revisions to bilateral tax agreements and economic penalties, such as restrictions on a country's banks operating abroad and on any foreign banks operating in the country on the black list.