Surreal but true: it’s people like me who are the true holders of the Blairite flame – not Tony Blair’s own fawning self-professed supporters. There is a pattern now: Blair’s public interventions instantly trigger spasms of rage on social media, which are derided by his followers as akin to deranged hysteria – as if the blood and chaos of Iraq and his work for serious human rights abusers since stepping down as Labour leader were trivial side issues. But his latest speech complicates things further, for it is an attack on the greatest defenders of his legacy: the left.

It is a point worth underscoring after this week’s debacle over the welfare bill. Tax credits are an innovation introduced under New Labour. Yes, less could have been spent on them if New Labour’s equally laudable minimum wage had been higher, had the party avoided the slump in wages that began in 2004, and had it invested in skilled jobs missing from our economy.

If Labour backs policies that introduce poverty as well as hammering low-paid workers, what indeed is the point?

But tax credits are a lifeline for millions of low-paid workers, helping to bridge the gap between low wages and the reality of existence. Many of the self-employed entrepreneurs championed by New Labour are affected too. This month the Tories introduced a budget that scaled them back. Labour’s response? To abstain, and back withdrawing tax credits from any supermarket worker’s child who might have two siblings rather than one. This is an act of vandalism perpetrated on New Labour’s legacy: and it was the left that opposed it.

Consider another of New Labour’s grand achievements: the war against child poverty. Poverty robs children. It damages their health, wellbeing, education and future. Under Blair and Brown, child poverty was reduced by a quarter – it was still at a rate higher than in the pre-Thatcherite era, but lives were transformed nonetheless. Eliminating child poverty is supposed to unite the Labour tribe like nothing else.

Compromises have to be made, New Labour once scolded the left, if Labour is able to come to power and help those who most need it. But, like scaled-back tax credits, the reduced benefits cap will achieve nothing more than driving children into poverty: tens of thousands more, at that. If Labour backs policies that introduce poverty by design as well as hammering low-paid workers – quite unlike what New Labour did – then what indeed is the point?

And then there’s the cornerstone of New Labour’s achievement – the thing that made it truly distinctive and different from Thatcherism: investment in public services. As both a principle and a reality, this achievement has been shredded. The myth that Britain’s economic plight was caused by Blair and Brown spending too much on schools and hospitals – every penny of which was backed by the Tories – was challenged by the left almost alone.

It is true that some of New Labour’s investment was undermined by handing over lumps of British public services to those driven by the profit motive. Still, the overall benefits were tangible. This investment is now being reversed through the biggest battery of cuts for generations: austerity backed by all too many of Blair’s staunchest supporters. It is the left that wants to preserve this investment, and build on it.

Many of the social blights of modern Britain are blamed on the number of immigrants New Labour let in, particularly from eastern Europe. Again, New Labour’s critics on the left have defended Blair and Brown from this charge. The failure to build affordable housing, create secure skilled jobs and prevent the slide in wages: here, the left says, are the real villains. But it isn’t the Polish careworkers and Lithuanian nurses who reached British shores thanks to Blair and Brown that are really to blame. Here again is a clear defence of New Labour’s record.

It is both a tragedy and a perverse irony that it is the left defending New Labour’s legacy, not New Labour’s own supporters. Certainly the left had criticisms at the time. It said the Iraq war would prove to be a calamity, though the truth is that the hideous consequences have been even worse than predicted. Our overdependence on the City of London and the failure to regulate banks properly were cruelly exposed.

Brown’s abolition of the 10p tax rate in 2007 was applauded as ingenious by much of the political elite at the time but resolutely opposed by the left. Spending should have been financed by increasing taxes on those with more than a bit of money to spare, and clamping down on those who avoided paying tax altogether. Who knows: if the left had actually been listened to on these issues, Labour could have saved itself from crippling long-term damage.

Ever since the disastrous election rout, some on the right of the party have been agitating for civil war, for the left to be taught a lesson. There has been little serious infighting over the last five years but relations between the left and right are breaking down rather fast. There was unity under Ed Miliband, the right claims, because we did not speak out, and look where it landed us. I know of one such Blairite MP who signed a letter backing rail re-nationalisation before the election, which shows how revisionist and opportunistic this line can be. But there is a truth they cannot escape: it is the left that is championing New Labour’s legacy, trying desperately to save it from the Tories. What a tragedy that many of Blair and Brown’s supporters do not want to do the same.