The world's richest one percent increased their fortunes by a total of $42 trillion over the past decade, Oxfam said yesterday, ahead of a G20 summit in Brazil where taxing the super-rich tops the agenda.

Despite this windfall, taxes on the rich had plummeted to "historic lows", the NGO added, warning of "obscene levels" of inequality with the rest of the world "left to scrap for crumbs".

Brazil has made international cooperation on taxing the super-rich a priority of its presidency of the G20.

At this week's summit in Rio de Janeiro, the group's finance ministers are expected to make progress on ways to raise levies on the ultra-wealthy and prevent billionaires from dodging tax systems.