The world is seeing the first stirrings of an emerging new architecture of global transparency in taxation which could, if pushed forward, help governments for the first time raise serious revenues from the estimated $21 trillion to $32 trillion sitting offshore.
Switzerland, with the tax havens of Luxembourg, Austria and Britain, is leading the charge to derail it.
The battle hinges on a powerful transparency principle called automatic information exchange.
According to this, governments routinely tell each other about the cross-border assets and income of one another's citizens so they can tax them appropriately.
This is the gold standard of transparency and the basis for the European Savings Tax Directive, which includes 42 European and other countries.
This multilateral scheme is riddled with loopholes, but it is already up and running. Amendments to plug those loopholes are being prepared.
A second pillar of the emerging architecture is run by the Organisation for Economic Co-operation and Development, a club of rich countries that contains several tax havens (including Britain, which partly controls a number of major tax havens, such as the Cayman Islands, the British Virgin Islands and Jersey).
The OECD scheme runs on a ridiculously weak transparency principle: information exchange on request. Here, you cannot make blanket information requests to a tax haven: you must ask, on a case-by-case basis.
That means you effectively have to know the information you are looking for - before you ask for it. Precious little information flows through these narrow pipes.
The OECD also runs a black, white and grey list system of tax havens. To get a sense of how useful this list is, note that in April 2009, when G20 leaders declared that ''the era of banking secrecy is over'' and asked the OECD to lead the charge, the blacklist was empty within just five days. The G20 asked the OECD to drain a swamp - and it has been handing out drinking straws.
The project helps at the margins, but is not a patch on the European scheme.
The United States is creating a third pillar under its Foreign Account Tax Compliance Act, which requires financial institutions to tell the authorities about foreign accounts held by American taxpayers.
Like the European system, it runs on the principle of automatic information exchange and, although originally set up unilaterally, the US is now pushing for reciprocal arrangements with other countries.
Over time, one would expect rising co-operation and cross-linkages between the trailblazing US and European schemes, and with others.
In August last year, Switzerland threw a huge spanner in the works. It signed bilateral tax deals - ''Rubik agreements'' - with Germany and Britain, based on a very different principle: wealthy people with Swiss accounts can preserve their secrecy and, instead, merely pay a one-off, withholding tax on assets, and a bit of future income.
''Trust us,'' say Swiss bankers - who have centuries of form helping the world's wealthy get around the rules of civilised society.
British tax authorities promised it would yield a tantalising bounty: a one-off £4 billion to £7 billion ($6.2 billion to $10.8 billion) for cash-parched, austerity Britain.
But the deals are riddled with catastrophic loopholes, some so egregious as to amount to signs saying: ''Evade me here''.
You can skip around them with discretionary trusts, foundations, insurance wrappers, offshore companies and more - or just shift your wealth to Singapore.
A forensic analysis by the Tax Justice Network last year revealed that Britain's Rubik would not raise even a 10th of the promised sum.
The analysis was sent to Her Majesty's Revenue and Customs, to the Swiss tax authorities, to Swiss bankers and to several tax advisers. None could refute it. HMRC's response? It has kept its head down.
The Rubik project is a Swiss swindle. If successful it would, in the words of Professor Itai Grinberg of Georgetown University, ''stifle the emergence of multilateral automatic information exchange''.
The Swiss Bankers' Association, which designed Rubik, has explicitly admitted that its original purpose was ''to prevent'' automatic information exchange: in other words, to kill the European Savings Tax Directive.
In particular, crucial and powerful amendments to plug the directive's loopholes are now held up because Luxembourg says it won't accept them if Germany and Britain (and now the tax haven of Austria, which has signed its own Rubik deal) get special bilateral treatment from Switzerland. This obstructionism was the plan all along.
EU tax commissioner Algirdas Semeta recently slammed Luxembourg and Austria over this political chess game.
''I cannot understand,'' he said, ''that anyone would make even more difficult the consolidation efforts by Greece, Ireland, Italy, Portugal and Spain and many other member states by holding up this issue.''
Thankfully, Germany's Bundesrat is widely expected to throw its Rubik deal out in a vote that was due to take place Friday evening Australian time.
The deal, forcefully supported by Finance Minister Wolfgang Schauble for reasons best known to himself, has been attacked by German opposition politicians.
A top Green party official called it ''a slap in the face for all honest taxpayers'' and the head of the centre-left Social Democratic Party, has accused Swiss banks of engaging in ''organised crime''.
If Germany rejects the deal, as seems likely, Austria will be easily dealt with, leaving Britain alone as the last big obstacle to progress in the greatest transparency project the world has seen.
British Chancellor of the Exchequer George Osborne, in his budget speech in April, described tax evasion and avoidance as ''morally repugnant''.
But his tax deal with Switzerland, as a fiscally useless spoiler, is a tax evader's dream.
The British government must repudiate it immediately. If it doesn't, the opposition Labour Party must commit to abolishing it - or hang its own head in shame.
Nicholas Shaxson is author of Treasure Islands: Tax Havens and the Men Who Stole the World.