Inequality, according to the World Economic Forum, is the greatest threat to the global economy.

President Obama has called it the defining challenge of our time. The aggregate incomes of the world's top 1.75% exceed the combined total of those of the bottom 77%, a chronic gap not seen for four decades. There is a growing consensus, from Pope Francis to International Monetary Fund head Christine Lagarde, calling for action.

Despite such high-status condemnation, the income gap has continued to widen through the global economic crisis. It is higher among the world's richest nations than before the financial crash.

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Across the UK, real incomes have been falling for years while corporate rewards have powered ahead. While inequality in Scotland is lower than in the UK as a whole, it is still strikingly higher than in Nordic countries such as Norway and Denmark.

Such levels of inequality should be economic red alerts. They make economies much more prone to crisis. The great surge in inequality since the 1980s not only blew us over the cliff in 2008; it also prolonged and deepened the downturn. It is sowing the seeds for the next crisis.

The clearest sign of the risks ahead is to found in what the Geneva-based International Labour Organisation has called the "dangerous gap between profits and people". While living standards have been falling, corporate profitability has reached new heights.

The world is awash with spare capital: a mix of corporate surpluses and privately-owned liquid wealth. In the UK, corporate cash piles have climbed to a record £165billion, more than one-tenth the size of the economy. American corporations are sitting on cash reserves of $1.45trillion, a remarkable 50% increase since 2010.

Before the crash, these surpluses were spent in ways that destabilised economies, distorting incentives and fuelling a boom in financial engineering that enriched the few while undermining the productive economy. During the crisis, and at present, these surpluses could have been used to launch a sustained investment and job-creating boom.

Even a portion could have raised Britain's sinking wage floor without a threat to competitiveness. Yet, instead, most of it was lying idle: "dead money", according to Mark Carney, the Bank of England Governor. It was this that fuelled the contraction in demand that led to the longest recession since the 1930s.

Now that recovery is belatedly under way, the risk is that these surpluses will be used again, not for much-needed investment, but to feed another round of high-risk self-enriching financial activity. Investment banks are already promoting a new version of the lucrative collateralized debt obligation, the financial product that wreaked so much havoc in the build-up to 2008.

In the UK, private equity groups hold more cash than at the height of the leveraged buy-out boom before 2007, one that culminated in the disastrous $100bn takeover of the Dutch bank ABM Amro by the Royal Bank of Scotland, creating mass losses ultimately paid for by taxpayers. Far from strengthening the productive economy, the "dry powder" held by groups such as Blackstone and the Carlyle Group will trigger an artificial boom in share prices while adding millions to the bank accounts of a few hundred executives, paid for by another round of staff lay-offs.

Despite the lofty speeches, the lessons of 2008 have yet to be learned. Economies built around poverty wages and huge corporate and private surpluses are unsustainable. As Larry Summers, former US Treasury Secretary and adviser to President Obama, has warned, today's dominant economic model seems only able to trigger growth through asset bubbles.

Creating a more equal distribution of the cake, with firms using these surpluses to finance a pay rise, is an economic imperative. Until we correct for these great imbalances, today's artificially created recovery will prove very short-lived.