European banks book €20bn a year in tax havens

However, there is a large discrepancy between the banks. HSBC, the largest bank, reports 58 percent of all its profits in a tax haven, while Swedbank is not active in tax havens at all.

Other major banks like Deutsche Bank and Standard Chartered report 21 and 30 percent respectively, a slight decrease compared to 2014 when country-by-country disclosure rules came into effect.

The study also reveals that branches in tax havens show an abnormally high 'profitability-per-employee' ratio.

For example, technically employees in non-tax havens yield a yearly profit of €65,000, while their colleagues in the British Virgin Islands and the Caymans net €2m and €953,000 per annum for their banks, respectively.

This suggests that the profits booked in tax havens have been shifted out of non-tax haven countries - which results in a considerable loss of income for the latter.

EU Tax Observatory estimates that a 25-percent minimum tax rate (the lowest current rate within the seven largest world economies), would net member states an extra €10-€13bn a year in tax revenue. In comparison, a 15-percent minimum tax rate would yield an additional €3 to €5bn in yearly income.

Progress in addressing a global minimum tax rate has been slow, but US president Joe Biden recently secured the backing of 130 countries for a figure of 15 percent, in a potential breakthrough.

"With a global minimum tax in place, multinational corporations will no longer be able to pit countries against one another in a bid to push tax rates down," Biden said .

The deal, which is supported by Germany and France, but opposed by Ireland and Hungary, is to be finalised in October and come into effect in 2023.