British-based charity Oxfam issued a rallying cry against inequality on Wednesday with the release of its "Even it Up" report, which found that the number of billionaires had doubled worldwide since the economic crisis.
The charity said the report, which is endorsed by humanitarian Graca Machel, former UN chief Kofi Annan and Nobel economist Joseph Stiglitz, was the "opening salvo" of a new campaign to force world leaders to take action.
"Far from being a driver of economic growth, extreme inequality is a barrier to prosperity for most people on the planet," said Winnie Byanyima, Oxfam International's executive director.
"Today wealth is trickling upwards, and will continue to do so until governments act," she added. "We should not allow narrow-minded economic doctrine and the self-interest of the rich and powerful blind us to these facts."
The report acknowledged that inequality between countries had fallen over the last 14 years, but claimed it was inequality within countries that mattered most, "as the poorest struggle to get by while their neighbours prosper".
According to the report, 70 percent of people live in countries where the gap between poor and rich has widened over the last 30 years while inequality of individual wealth has become even more extreme.
It calculated that the wealth of the world's 85 richest people grew $668m each day.
"If Bill Gates were to cash in all of his wealth, and spend $1m every single day, it would take him 218 years to spend it all," it said.
"Since the financial crisis, the ranks of the world’s billionaires has more than doubled, swelling to 1,645 people."
Stiglitz warned that today's level of inequality "harms our economies our societies, and undermines our politics."
The report called for drastic action to reverse the trend, which it blames on "market fundamentalism" and the capture of legislatures by wealthy elites.
"The potential benefit of curbing runaway wealth by even a tiny amount also tells a compelling story," it said.
"Oxfam has calculated that a tax of just 1.5 percent on the wealth of the world's billionaires, if implemented directly after the financial crisis, could have saved 23 million lives in the poorest 49 countries by providing them with money to invest in healthcare.
"In 2014 a tax of 1.5 percent could fill the annual gaps in funding needed to get every child into school and deliver health services in those poorest countries," it added.
The charity argued for a global focus on taxing wealth instead of income, the closing of tax loopholes that favour the rich, free at point of use public services and medicines and an increase in the minimum wage.