A pasting from Sir John Major might be likened to being savaged by a garden gnome. But last week, in his understated way, the former PM – more known for droning than invective – hit home. The welfare secretary's plans, he said, would run into trouble "unless he is very lucky, which he may not be, or a genius, which the last time I looked was unproven". Iain Duncan Smith's ratty response, about the "intellect … that delivered us the cones hotline", made him sound almost as rattled as Margaret Thatcher after the dead sheep bit back in Geoffrey Howe's resignation speech.

Until now, the bulk of the press and the Conservative party alike have hailed IDS as a zealous reformer, a determined man with a plan. He sees himself the same way – squaring up to the chancellor whenever required to protect the cherished universal credit, which, with apparent sincerity, he suggests will iron out every welfare perversity, and banish a dependency culture. He is a plausible salesman for this plausible-sounding proposal to sweep away six benefits in favour of one streamlined system. Until now – with the government prevailing in the polls in his field – he has been blessed, to a degree exceptional in modern politics, with the benefit of the doubt.

There have always been sceptics, gently pointing out that Mr Duncan Smith was not – as he may believe – the first to spot perversities in social security. Rather, ministers since Norman Fowler in the mid-1980s have been merging benefits, and trying to ease the poverty trap. Most of them, however, were modest enough to realise that they were not so much definitively solving a problem, as resetting the balance between inherently competing objectives – providing for people because they are poor, rewarding them for earning a wage, and containing calls on the public purse. With a fair wind and a steady steward, universal credit might have simplified administration, and refined these trade-offs to the good. But cuts representing a quarter of the working-age benefit bill redoubled the risks. The government's unintelligible decision to invite every town hall to invent its own means test for council tax without any regard for how it fitted in with Mr Duncan Smith's new architecture made even more daunting his hopes of pulling off a practical success.

Too few have worried about such details for too long. But the time for fighting talk is past – it is time for Mr Duncan Smith to do. And, as facts begin to intrude on his theory, the great reformer is slowing the pace. The roll-out of the new credit "to London" this week, did not roll beyond Hammersmith. As we report today, whispered anxieties in Whitehall about the whole thing falling over have now risen to a pitch where plans to write off up to £119m of preparatory work already done are being actively considered, with the possibility that the IDS revolution will slow to such an evolutionary timescale that it will only have touched 0.2% by the time of the next general election, and the possible end of his five-year term.

This slothlike progress may cause blushes, but it is preferable to the alternative of pressing on regardless of operational risks, as the Department for Work and Pensions has often done under Mr Duncan Smith. This week alone saw two past episodes of that habit return to haunt it. First, the enactment of "legislation" to overhaul disability living allowance was delayed. Rather than identify the losers to, and face the scrutiny of, parliament, IDS rammed through sweeping enabling powers to cut DLA as he liked, trusting himself to sort the details later, behind closed doors. Alas, he has been unable to do so on time. Second, regulations to force the unemployed to toil unrewarded were ruled unlawful by the supreme court. Rather than taking this as admonishment for his failure to take the time to write lawful rules, in the looking-glass world of the welfare secretary, the judgment was a triumph because it stopped short of denouncing his workfare as slavery. Perhaps this sort of audacity qualifies as genius of a sort.