But announcing the policy this morning has also given Alistair Darling and Vince Cable a chance to very publicly denounce it later today. We've already had a preview of what's likely to form the central thrust of Darling's counterattack, courtesy of Patrick McFadden on GMTV earlier. He accused the Tories of "spraying money around," adding that, "I wonder what happened to the Conservative party that talked about credibility on the deficit." And, as for Vince Cable, the Lib Dems' commitment to cutting the deficit entirely through spending cuts probably means that he can't echo McFadden's sentiment – so I imagine he'll simply point out that his party already have some significant tax-cutting pledges of their own.
Much will depend on how the Tories decide to fund their policy. Presentationally speaking, it's encouraging that they're not going to raise the necessary £5 billion through tax increases elsewhere – but, rather, by cutting some of Labour's many spending "projects". Given how our public finances have been handled, it shouldn't be too difficult for Osborne & Co. to find something that both voters and the government won't miss. But we'll discover whether he succeeeds, when we hear more details, in the next half-hour or so.