A study of Europe's largest banks by Oxfam has concluded that the continent's 20 biggest banks all use jurisdictions with favorable tax and regulatory rules to avoid paying their full liabilities, draining public finances by in the process.

The 52-page report, the first in-depth analysis of the conduct of Europe's 20 largest banks on a country-by-country basis, highlights a clear pattern of tax-dodging, with around €25 billion (US$27,3 billion) siphoned to tax havens annually, rather than the coffers of national exchequers.

Europe’s 20 biggest banks are using tax havens on an industrial scale: https://t.co/OFxOq53vQX #endtaxhavens pic.twitter.com/UfWOwdFdSI

— Oxfam International (@Oxfam) March 27, 2017​

Tax havens such as Bermuda, the Cayman Islands and the Isle of Man are key destinations for fleeing bank profits, with the report sardonically noting bank employees working in tax havens appear to be four times more productive than an average full-time bank employee. On average, a bank employee generates a profit for their company of US$50,000 per year, but employees in tax havens make an average US$186,000 per year. An employee of Italian bank Intesa Sanpaolo based in a tax haven appears to be 20 times more "productive" than a worker at the bank's Italian branches.

"These very high profits per employee in tax havens cannot reasonably be a reflection of the skills and efficiency of employees based in tax havens, but rather indicate reported profits are unusually high there," the report says.

Nonetheless, Oxfam makes clear the money also ends up elsewhere within EU member states such as Luxembourg, with banks such as Barclays using the Grand Duchy to pay effective tax rates of around 0.2 percent.

ROI & NI Press Release re new Oxfam report 'Opening the vaults: the use of tax havens by Europe's biggest banks': https://t.co/PH2NU2xUwm — Oxfam Ireland Media (@Media_OxfamIRL) March 27, 2017​

Ireland is another popular destination, as banks can circumvent tax liabilities by basing their European headquarters in the country. While Ireland has headline corporation tax rates of 12.5 percent (the second-lowest in the European Union alongside Cyprus), the country maintains double taxation agreements with a variety of virtual tax havens, which allows firms based there to shift profits to jurisdictions such as Panama, meaning they often don't even pay Ireland's humble rates.

A February 28 Oxfam Ireland report indicated companies route as much as US$100 billion out of Ireland annually via this ruse.

The use of tax havens has even enabled banks such as BBVA, RBS, Santander, Societe Generale and UniCredit, to reap profits in excess of their reported annual turnovers.

Top tax havens in terms of reported profits for Europe's largest banks. Hong Kong leads, followed by Luxembourg. @oxfam @TaxJusticeNet pic.twitter.com/9ZdKZJ7kpC — Hera Hussain حرا (@herahussain) March 27, 2017​

In an ironic twist, Oxfam sourced its information from official EU data — since 2015, all banks based in the EU have been obliged to publicly report profits earned and tax paid on a country-by-country basis, the only sector required to do so — perhaps a suggestion the bloc's ongoing push for financial services openness has not been successful in changing the sector's behavior.

"The urgent need now is to extend public country-by-country reporting to all sectors of the economy. If tax transparency is extended to all sectors, it will be easier for governments to clamp down on tax dodging and to repatriate lost tax revenues that could be used to fight inequality through investment in healthcare, education, social protection and job creation," the report said.

However, Oxfam's research suggests the banks aren't all as bad as one another — while all 20 had operations in tax havens, some were much more active in using them to avoid paying tax than others. The charity believes this demonstrates it is quite feasible for a bank to act ethically, despite market pressures.

European banks booked €628 million profits in tax havens where they employ nobody. Time for public #cbcr @EUCouncil https://t.co/XZfhTg6FCL — Markus Meinzer (@markusmeinzer) March 27, 2017​

It also follows revelations in 2016 that European politicians and criminals use Panama to hide their money, with the exposures implicating HSBC, Societe Generale, Credit Agricole, BNP Paribas and Santander, also implicated in Oxfam's recent report.

Last April, the EU Commission proposed legislation that requires multinationals to reveal their tax data, although campaigners claim the plan has been significantly diluted, with the proposal excluding up to 90 percent of the business operating in the EU as it only applies to those with annual turnovers of at least €750 million (US$816 million).