No wonder there is public outrage at MPs' expenses. Now we know from this week's figures what has happened to ordinary incomes, every average earner sees the yawning gap between themselves and their rulers. The gap between the top 10% who earn more than £40,000 and the rest has widened, and people are angrier. In such an unequal country, expenses that may seem normal for top taxpayers – £6,000 for Gordon Brown's cleaning – look extravagant to median families who live on £393 a week.

MPs have been caught in a crucible between two social worlds growing increasingly far apart – worlds they should have done more to equalise. For years they have been warned that growing inequality is profoundly socially dysfunctional. For years, Tony Blair and Gordon Brown said inequality didn't matter. All that mattered was that the poor should be raised nearer the middle. Alas, this week's figures show that not even that happened. The middle stagnated while the poor have fallen behind. So now the social divide has jumped up and bitten Labour. People can see how far their rulers have grown from ordinary lives. In an ironic quirk of political timing, the angry response of many will be to vote Conservative instead.

There was something melancholy about yesterday's celebration of the opening of the 3,000th Sure Start children's centre. It is a pearl in the wreckage of Labour's legacy, and another reminder of all Labour might have done had it been devoted singlemindedly to the "fairness" it proclaimed. As it is, there are still more golf courses than there are children's centres.

Meanwhile, in Labour's decade, billionaires' wealth quadrupled and three out of five of them paid no income tax. Yet in the five years before the crash, average incomes barely changed – and the poor became poorer. No wonder the public grew sceptical of official statistics that proclaimed GDP "growth" when it was only for the few, not the many.

This week's income figures are so shameful that Labour MPs are left gasping. How can inequality be higher than under Margaret Thatcher, the highest since records began? Ask Labour MPs why they are in politics and they will say it's all for a fairer society. Labour this week sent out letters asking people to join the party for a "fairer" Britain. Instead they have created a less fair one. Now the public sees their expenses, not only MPs, but the process of democracy itself is imperilled by public disgust. What a dangerous gift to those Westminster outsiders, the BNP.

The verdict on Gordon Brown's tenure of the Treasury is as bleak as it could be. Was he the worst chancellor, with the worst economic advisers? Replay the hubris of his every budget speech and shudder. History may judge him and Blair equally as peddlers of a chimera, having-it-all without counting the cost, living on the City's fairy money. They were elected to spend on public services after years of growing public squalor, but they did it without raising the tax to pay for it. They offered voters "world-class" everything, though world-class inequality is what we have now.

Brown would say hindsight is a fine thing: no one foresaw a global bank crash creating a recession to rival the 1930s. He would say that even frugal and prudent states like Germany and Japan have suffered as badly or worse than us. But there is just no excuse for the way he let this inequality swell in the good times. Our debts are now so serious that there will be cuts. It has let the Tories make national debt the national issue. Pretending our grandchildren will be paying it off resonates brilliantly in the opinion polls – though that, too, is a chimera. True, we can't keep borrowing, but much of the debt will melt away through growth and inflation over the next 20 years. (See Michael Blastland's excellent explanation on the BBC website).

However, we may soon be brutally reminded that despite it all, Labour is still "fairer": worse happens to income and poverty figures under the Tories. Under Thatcher, child poverty rose sharply; Labour has reduced it by 600,000. Tax credits mitigated forces pulling towards even greater inequality. Labour was running up a down escalator, failing to tax enough or divert money from elsewhere. What if Labour had never gone to war or "punched above our weight" on the foreign stage with aircraft carriers and Trident? What if it kept the Olympics to its promised price, hadn't created ID cards, or doubled the prison population, or wasted billions on the "war on drugs"? If only they really had put "fairness" centre stage, and dared to believe that they could make the political weather. What a wretched week of self-inflicted trauma this has been, crowned by MPs' expenses leaving voters disgusted with the entire ruling class as elections approach.

When parties die, the evil that they do lives on. But in future Tory times we will be better able to look back with regret on the good Labour did. If children's centres survive, they will stand as a good monument, holding out the best hope yet of rescuing families in trouble before children arrive in school too late to be helped. Pay no attention to sneers from those who would cut them: the 2.4 million families who use them are seeing children develop better socially. The great test of David Cameron's seriousness about "broken Britain" will be whether he promises to nurture them.

This week marks 30 years since Thatcher walked into No 10, creating the myth that it marked an epochal change in attitudes. It didn't. It marked the day when Britain's dysfunctional electoral system allowed a small rightward shift to let in an unrepresentatively radical party. When unions over-reached themselves, 44% voted for her but 56% still voted against. British Social Attitudes showed year after year that people stayed wedded to the welfare state, the NHS, the BBC and social security. The majority always voted to the left of her, and her savage cuts made her the most unpopular PM to date, saved only by the left's exceptional disarray.

So if Cameron hopes this is a tipping point, he would do well to remember what pollsters such as Mori's Ben Page keep reminding us of: that most people's values hardly change at all. They may throw Labour out for all its failings, but a majority remain essentially social democrat at heart. Labour, however, will need to earn back the right to claim to be the champions of "fairness".