After Labour used Mumsnet to attack  the Conservatives' plans to reduce tax credits, the Tories have hit back with an advert of their own.
The Labour ad, you may remember, claimed that the Tories would abolish tax credits for all families with incomes over £31,000, rather than £50,000. The Tory ad rejects this claim as "complete spin" and, in a related blog post , the shadow work and pensions secretary, Theresa May, goes further and describes it as a "lie".
So who's right?
Labour claimed that figures from the Institute for Fiscal Studies show that lowering the threshold to £50,000 would raise only £45m and not, as George Osborne claims, £400m. To raise that sum, the shadow chancellor would have to lower the threshold to £31,000, said Liam Byrne , Chief Secretary to the Treasury.
Here's what the IFS said:
Without access to HMRC's data, it is not possible for us to say precisely how much money would be raised by the Conservative Party's proposal having allowed for incomplete take-up, but it can be stated confidently that it would be less than £0.4 billion (because that would require lowering the threshold to £31,000), but more than £45 million (which is what would be raised if the threshold at £50,000 were replaced by a cliff-edge, as this is the total amount to which families with incomes exceeding £50,000 are entitled).
So the Tories are wrong to claim that their plan would raise £400m but Labour is equally wrong to claim it would raise just £45m. But after their disingenuous poster  on Labour's "death tax" earlier this week, the Tories aren't really in a position to cry foul.