Leading article: Live up to your own slogan, Dave

"All in this together" must count as one of the worst slogans dreamt up by supposedly intelligent people. More effectively than any lines devised by the Labour Party, it invites cynicism and draws attention to one of David Cameron and George Osborne's weak points. Namely, how hard it is to believe that these men from such fortunate backgrounds understand the hardships of people on low incomes.

As part of the decontamination of the Conservative brand, Mr Cameron earned a surprising standing ovation at his 2009 conference speech for castigating Labour for allowing the gap between rich and poor to widen. But this rebranding never seemed to go very deep, and was always going to be tested by the reality of government.

As we report today, the incomes of the very richest, the top one-thousandth, have risen steeply and will rise for the foreseeable future. Over most of the income distribution, the trend towards inequality is much less marked, but, to quote Lord Ashburton on the influence of the Crown in 1780, inequality "has increased, is increasing, and ought to be diminished".

Let us be clear, though, about what is happening and why it is a problem. Official figures confirmed last week that incomes in Britain became more unequal under Labour. However, the big increase in inequality occurred under Margaret Thatcher in the 1980s, while the increase under Labour was half what it would have been "if the 1997 tax and benefit system had simply been uprated in line with prices", according to the Institute for Fiscal Studies.

Labour's policies of redistribution were not enough to reverse the trend, but achieved valuable reductions in child poverty especially. It was all very well for Mr Cameron, in opposition, to criticise Labour for failing to cut poverty further and for not doing enough to tackle welfare dependency, but Iain Duncan Smith's welfare reforms will make inequality worse, certainly in the short term.

At this point it is worth restating the basic case for greater equality. The size of the gap between the top and bottom of a society matters. Once basic needs for food, clothing and shelter have been met, it becomes possible to consider social cohesion. A society worth the name needs to feel that its constituent parts share something of a common life, and that is made ever harder if the gap in income or wealth is too great. As philosophers including John Rawls have explained, a just society depends on the possibility at least that we could be "all in this together".

The other part of Mr Cameron's attempt to distance himself from Baroness Thatcher's "no such thing as society" is just as flawed. "There is such a thing as society," he declared, "only it is not the same as the state." He filled the gap with the "Big Society", which is a good, if non-political, idea. Or it would have been if public spending had been sustained. At a time of the deepest fiscal retrenchment since at least the 1970s, however, it is a fundamentally unworkable idea.

Our ComRes poll today finds that more people say that they have heard of the Big Society but don't know what it means than three months ago. This is remarkable evidence of a failure of communication. The reason for this failure is suggested by an earlier Independent on Sunday poll which found that, by a majority of two to one, people agreed that the Big Society is "merely cover for public spending cuts". It does not matter whether or not that is the Government's intention; it will be impossible to win support for the Big Society while volunteers feel they are being expected to make up for state funding.

The other problem with the Big Society identified by the Rennard report, as we disclose today, is that people are more likely to volunteer in better-off neighbourhoods. Thus the risk is that the Big Society becomes either trendy and vacuous "social enterprise" or patronising charity for the poor.

It would be wise for Mr Cameron to forget about the Big Society for a long time and perhaps return to the theme, if he is still in No 10, in better fiscal circumstances in several years' time.

In the meantime, if the Prime Minister wants to make good on his rhetoric of "such a thing as society", he should study our list of the myths about why executive salaries of 145 times average earnings are justified, and should require bankers and the super-rich to make a fair contribution, and to be "all in this together" too.