This is an important book with an extraordinarily important message, conveyed by its title. The book has clearly resonated with politicians, policy-makers, academics, researchers and many others: the authors have achieved something like superstar status, and not just within the narrow confines of the social policy world, embarking on what might be regarded as the equivalent of a world tour in the past year or so, speaking to the media, at conferences and seminars on literally hundreds of occasions.

Given that the issue of equality is so important to so many, the question about this phenomenon is less about ‘why?’ than about ‘why now?’ I recall Wilkinson’s first forays into this area of debate in the mid- to late 1980s.  The New Zealand government, having embraced Thatcherite politics and economics, had created the most unequal society within the OECD family of countries and one corollary of this was that it had increasing health inequalities and, for example, the highest suicide rate in the OECD. Wilkinson, rather more tentatively then, had suggested that the two trends were linked. Politicians nodded – and moved on. Now, 25 years later, the same message, albeit supported by a much more wide-ranging and robust body of evidence, has created a substantial political stir. I asked Wilkinson at a recent public presentation why he thought it had done so: but he was also at a loss to know why.

Of course it remains to be seen as to whether it makes a difference in political terms. New Labour came to power in the UK in 1997 promising to deal with the deeply unfair society which was the legacy of 18 years of Tory rule. For the first few years, it looked as if their policies on child poverty and manipulating the tax system was having an impact. However, this was a false dawn. Certainly hundreds of thousands of children have been lifted over the poverty threshold, but these were the easy ones, being just below the poverty line; and that line was itself set at a scandalously low level as endless research since the days of Rowntree has shown. Meanwhile, top incomes and wealth were left unattended and, as the recent report of the National Equality Panel, commissioned by Harriet Harman and chaired by John Hills, has shown, broadly we are back where we were in the late 1990s with disgracefully high levels of inequality, not just in terms of income but in terms of outcomes for every area of public welfare.

Despite what we now know about what the banks and other financial services have done, Goldman Sachs can announce that in the first quarter of 2010 the average bonus paid to their employees was more than £1,000,000 – and that was the average! Goodness knows what the highest paid in the company were getting – but the announcement passed with barely a political murmur. The best the Tory party can do is to suggest that top salaries in the public sector should be capped at 20 times the average salary of employees – which would affect a handful of people – whilst it is silent on the private sector, which, of course, is where the real problem lies. The Labour mantra continues to be about economic growth and that misses the point too, because the issue is not about everyone getting relatively richer but about the differences between rich and poor.

Perhaps this climate has generated the interest in the book, but only time will tell whether its message has any real long-lasting political purchase. So what is the message?

Wilkinson and Pickett review at length the international evidence for a wide range of social issues – mental health, drug use, physical health and life expectancy, obesity, educational performance, teenage births, violence, imprisonment and social mobility – to demonstrate that the growing wealth of countries does not in itself tackle what most countries still recognise as serious social ills. What is required is a concerted attack on inequality in all its forms. The authors do not argue that, historically, there has not been a trend towards equality – they cite the abolition of slavery, the extension of the franchise, the abolition of capital and corporal punishment, and demands for greater equality of opportunity as evidence of this trend over the past centuries – but that, within societies, those which still have substantial differences in income and wealth, most of all, will be those afflicted with the manifestations of unhappiness, depression, ill-health, high levels of obesity (ironically more so amongst the poorer than the richer) and so on. And this is as true at the level of the state as it is at an individual level. Wilkinson and Pickett show, for example, that the most unequal societies are those that are most belligerent on an international stage.

The gains of having more equal societies are enormous. Anyone who has studied comparative social policy will know that the more egalitarian societies such as the Scandinavian block are those, despite relatively high levels of taxation, which “live well, with high living standards and much better social environments”. And “if the United States was to reduce its income inequality to something like the average of the four most equal societies (Japan, Norway, Sweden and Finland), the proportion of the population feeling they could trust others might rise by 75% with matching improvements in … the quality of community life”, and with correspondingly huge reductions in rates of mental illness, obesity, imprisonment, teenage births and premature deaths. The same outcomes would apply to the UK which is now one of the most unequal OECD countries.

To reach this goal requires, the authors argue, the creation of a sustained movement based, most of all, on widespread public understanding (and they offer some suggestions for how this should be done, including the establishment of a Foundation for promoting their ideas about equality). This movement goes way beyond those in formal political power, but it has to bring its pressure to bear on those in power. It would require a political manifesto which goes well beyond any on offer at the recent General Election with a preparedness to face down the arguments, for example, that much higher – and redistributive – taxation would lead to capital flight.  There are no political parties currently on offer which would adopt this programme: but, perhaps, armed with the overwhelming evidence in this book, we can not only hope that one might emerge but join that movement to make it do so.