The number of billionaires in the world has more than doubled since the financial crisis began, in a surge of inequality that one charity said could "set the fight against poverty back by decades".
The number of dollar billionaires increased from 793 to 1,645 between 2009 and 2014, according to Oxfam, which said inequality between rich and poor is "spiraling out of control".
Despite the recession that has seen governments cut welfare spending, the 85 richest people on earth saw their collective wealth rise by £150 billion in the last 12 months - around £415 million a day, or almost £333,000 a minute, the charity's latest report said.
Earlier this year, it said that these 85 people had access to wealth equal to that of the poorest half the world's population.
If all the world's billionaires had been taxed at a rate of 1.5% on their wealth over 1 billion US dollars in 2014, it would have raised £46 billion - enough to get every child into school and deliver health services in all of the world's poorest countries which would cost around half that figure - said the report.
Oxfam's chief executive Mark Goldring said: "Inequality is one of the defining problems of our age. In a world where hundreds of millions of people are living without access to clean drinking water and without enough food to feed their families, a small elite has more money than they could spend in several lifetimes.
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"The consequences of extreme inequality are harmful to everyone. It robs millions of people of better life chances and fuels crime, corruption and even violent conflict. Put simply, it is holding back efforts to end poverty.
"Governments around the world have been guilty of a naive faith that wealth going to those at the top will automatically benefit everyone. That's not true - it is their responsibility to ensure the poorest are not left behind."
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The report said there are 16 billionaires in Sub-Saharan Africa, where 358 million people live in extreme poverty, while in South Africa inequality is now "greater than it was at the end of apartheid".
If African levels of growth and inequality continue on current trends, it is estimated that the continent's poverty rate won't fall below 3%, which is the World Bank's definition of eradicating poverty, until 2075.
The report also marks the launch of an Oxfam campaign that challenges governments to follow a plan to reduce inequality by clamping down on tax dodging, investing in free healthcare, legislating equal pay, agreeing a global way of tackling inequality and changing taxation from working and consumption to capital and wealth.
Mr Goldring added: "Extreme inequality is far from being inevitable - it is the result of political choices and economic fashion, kept in place by a wealthy elite whose influence helps keep the rules rigged in their favour. Too often, the 'invisible hand of the market' is used as an excuse to pick the pockets of the poor.
"In countries around the world, a wealthy minority is taking an ever-increasing share of the pie. This is not just an issue of fairness, but in a world where people are dying of hunger or because they can't afford healthcare, it becomes an issue of life and death."
Oxfam said billionaires had too much money to spend in one lifetime. If Carlos Slim, the world’s richest man, were to cash in all his wealth and spent 1 million US dollars every day, it would take him 220 years to spend it all, it said.
Responding to the report, Bank of England chief economist Andrew Haldane said: "In highlighting the problem of inequality, Oxfam not only speaks to the interests of the poorest people but also the wider collective interest.
"There is rising evidence that extreme inequality harms, durably and significantly, the stability of the financial system and growth in the economy. It slows development of the human, social and physical capital necessary for raising living standards and improving well-being. That penny is starting to drop among policymakers and politicians."
Nelson Mandela's widow Graca Machel said: "The last decades have seen incredible human progress across Africa and the world. But this progress is under threat from the scourge of rapidly rising inequality.
"Addressing the gap between the richest people and the poorest and the impact this gap has on other pervasive inequalities between men and women and between races that make life for those at the bottom unbearable is an imperative of our times. Too many children born today have their future held hostage by the low income of their parents, their gender and their race.
"The good news is that this growing inequality is not inevitable. It can be resolved."Suggest a correction