In 2011, the Occupy Movement launched in New York in protest at the increasing wealth of the ‘1%’ – at the expense, it was claimed, of everyone else. After the global economic crisis, many campaigners demanded that multinational corporations and wealthy financiers – ‘fat cats’ – should contribute more to society through taxation. In 2014, the left-leaning French economist Thomas Piketty had a surprise international bestseller in 2014 with Capital in the Twenty-First Century, which suggested that inequality was likely to continue to grow, while UK aid charity Oxfam caused a stir with the claim that the 85 richest people globally have as much wealth as the poorest half of the world’s population.

But concerns about inequality are by no means limited to radicals. In 2013, Christine Lagarde, managing director of the International Monetary Fund (IMF), declared ‘Excessive inequality is corrosive to growth; it is corrosive to society.’ It is a theme that has been popular among many politicians, too. In 2012, US President Obama called inequality ‘the defining issue of our time’. Sweden’s prime minister, Stefan Löfven, has linked inequality to the rise of the far-right, claiming ‘the increasing support of the Swedish Democrats is not a result of growing racism or even widespread xenophobia, but rather a result of wider and wider gaps in society’.

The Spirit Level: Why More Equal Societies Almost Always Do Better, published by two British academics in 2009, became a must-read book for many politicians and think tanks. The authors, Richard Wilkinson and Kate Pickett, argue that inequality has ‘pernicious effects’ on societies, including ‘eroding trust, increasing anxiety and illness, (and) encouraging excessive consumption’. Yet critics of The Spirit Level have argued that the authors were selective in their use of data and that inequality is a poor predictor of social problems.

Other critics of the discussion around inequality argue that poverty, not inequality, is the real problem. Even on this question, there is controversy. A common measure is relative poverty, which looks at the number of people whose income is below 60 per cent of a country’s median income. But is relative poverty really an appropriate measure? For example, Sweden is widely recognised to be a more equal society than the US. But as one commentator notes, ‘the Swedish poverty rate… is much lower than the US poverty rate. But equally other research tells us that the actual living standards of the bottom 10 per cent of Sweden are almost exactly the same as the living standards of the bottom 10 per cent of the US.’

Should we be worried about inequality as well as poverty? Does inequality have effects on society that go beyond material disadvantage? Why have politicians become so keen on tackling inequality today?