A gigantic years-long tax scam saw banks drain 55 billion euros ($63 billion) from national treasuries in Europe, a far larger sum than previously thought, media from across the continent reported yesterday, reports AFP from Frankfurt.

The so-called "cum-ex" deals relied on complex tax trickery that allowed owners of shares to claim several times over refunds for tax paid only once on dividend payouts -- effectively syphoning off taxpayers' money into investors' pockets.

So far estimates of the damage had ranged from 5.3 billion euros according to the German finance ministry to 30 billion, according to press reports.

But a joint investigation by European media outlets has concluded that at least 55.2 billion euros were stolen from 11 countries: Germany, France, Spain, Italy, the Netherlands, Denmark, Belgium, Austria, Finland, Norway and Switzerland.

Reportedly conceived by well-known German lawyer Hanno Berger, the cum-ex method relies on several investors buying and reselling shares in a company amongst themselves around the day when the firm pays out its dividend.