Whichever Conservative first came up with the line that "no out-of-work family should receive more in benefits than the average family receives from going out to work" probably deserves some sort of prize. The policy to which it refers - the benefit cap of £26,000 (£500 a week) - has been framed so as to make reasonable disagreement appears impossible. Who can argue that it should pay more to be on welfare than in work? (Although the cap takes no account of the in-work benefits claimed by families.) It’s unsurprising, then, that the measure is the coalition’s most popular. A YouGov poll published earlier this year found that 79% of people, including 71% of Labour voters, support the cap, with just 12% opposed. But while politically astute, the cap, which was introduced nationally in July, is perhaps the most flawed of all the government's policies.

A study of its effects in Haringey, one of the boroughs where it was piloted from April, offers new evidence of why. While the cap is saving the council £60,000 a week after 747 households had their benefits reduced, it is costing nearly as much to manage. The council is currently spending £55,000 a week on Discretionary Housing Payments to help claimants meet their rent and thousands more on additional welfare and employment support. None of this should be surprising. As a leaked letter from Eric Pickles's office to David Cameron warned in 2011, the measure "does not take account of the additional costs to local authorities (through homelessness and temporary accommodation). In fact we think it is likely that the policy as it stands will generate a net cost. In addition Local Authorities will have to calculate and administer reduced Housing Benefit to keep within the cap and this will mean both demands on resource and difficult handling locally."

At the same time, there is little evidence that the cap is achieving its stated aim of moving claimants into work (principally because few choose to live "a life on benefits"). Just 74 of the 740 households affected have found work, a number no greater than one would expect without the cap given the regular churn of claimants. In many cases, the lack of affordable childcare continues to represent a barrier to employment. Indeed, by requiring councils to relocate families hundreds of miles away, the cap actually reduces work opportunities by forcing them to live in an area where they have no employment history.

But to judge the cap on these terms is to misunderstand the government's motives. The cap is less a serious act of policy than a political weapon designed to trap Labour ("the welfare party") on the wrong side of the argument and to perpetuate the belief that the unemployed are to blame for their own misfortune. On this basis, lamentably, it is working just as intended.