THE word "politics", Robert Reich tweeted caustically the other day, comes from the Greek root poli (meaning many) and tics (small, blood-sucking insects).

It was typical of the pithy tweets fired off by the charismatic, outspoken academic at Berkeley, California who, in the 1990s, was Labour Secretary under Bill Clinton. He has for decades agonised over America's growing income inequality, hammering home the message that it poses a severe threat to economy and democracy.

Reich's flow of tweets on economic and political matters makes for arresting reading. January 30: "Now not time to cut public spending. Austerity economics a cruel hoax." January 27: "Britain's austerity economics is complete disaster. Its economy shrinking". February 4: "Rarely in history has so much been spent by the very wealthy seeking intellectual and moral justification for their indefensible wealth."

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Another post: "Economy heading toward recession because most Americans' take-home pay shrinking, can't buy enough to keep ec[onomy] going" is echoed in Reich's latest project, a documentary, Inequality for All. A measure of its success, and of Reich's persuasive rhetoric, is that it won the special jury prize at the Sundance festival.

It's been described as An Inconvenient Truth for the economy. Reich has a gift for making complicated economic subjects digestible and making us challenge our assumptions. His figures are stark: "42% of children born in poverty in the USA will stay there," he says. "In Denmark it's 24%. Even in Great Britain, where they still have an aristocracy, it's 30%."

Nor does Reich see inequality getting less pronounced soon. "Where America leads, sadly the rest of the world follows. This same thing is affecting people all over the world," he said last weekend. "If nothing is done to reverse this trend, Britain will find itself in the same place as America in a few years' time." The film interviews economists and politicians, but also talks to ordinary people who have been left behind in the income race while the super-rich accelerate out of sight. Their impoverished struggles have reduced audiences in tears. Reich hopes the documentary will trigger a debate. It would help us all if his wish was granted.