Business 4 January 2010 On inheritance tax there is a "credibility gap" Cameron's plan remains unfair and unfunded Sign up for our weekly email * Print HTML David Cameron has denounced Alistair Darling's 148-page dossier on the "credibility gap" in the Tories' spending plans as "complete junk from start to finish". So are the Tories' spending commitments fully costed? Here's one that isn't. Cameron claimed again today that sweeping cuts in inheritance tax could be paid for by "taxing the non-doms". The party's pledge to raise the inheritance-tax threshold -- currently £325,000 -- to £1m would cost £3.1bn a year. Cameron hopes to raise this amount by charging non-doms £25,000 a year to live and work in the UK. The Tories estimate that about 150,000 residents would pay the levy, raising £3.5bn and funding cuts in inheritance tax and a rise in the stamp duty threshold to £250,000 for first-time buyers. But the Tory proposal overestimates the total number of non-doms. The latest HMRC figures show that there are only 120,000 currently registered. Ken Clarke was admirably honest when he conceded: "We don't know how many non-doms will be here; we don't know how much our policy of raising fair taxation from foreigners who work in this country will raise." It's a pity his leader can't be. The commitment to cut inheritance tax could yet become politically toxic for the Tories, particularly if the suspicion that a Cameron government would increase VAT grows. History teaches us that when in need of revenue, the Tories raise VAT, the most regressive tax of all. It was Margaret Thatcher who almost doubled VAT from 8 to 15 per cent in 1979 in order to slash income tax and it was John Major who raised VAT by 2.5 per cent to its current level of 17.5 per cent. Over at Comment Central, Daniel Finkelstein astutely notes that Darling himself still refuses to rule out raising VAT to 20 per cent. The Chancellor's plan to do so in the pre-Budget report was overruled by Gordon Brown. By contrast, Ed Balls (writing outside of his brief) has accused the Tories of secretly plotting to increase VAT and has attacked George Osborne for refusing -- like Darling -- to rule out a rise. Balls might be keen to use these lines on the campaign trail, but VAT could yet become a dividing line between him and the man he still longs to replace. Follow the New Statesman team on Twitter › Defending the Danish cartoonist George Eaton is political editor of the New Statesman. Subscribe from just £1 per issue More Related articles Is Labour really as doomed as it seems? The polls have got it wrong before Two referendums have revived the Tories and undone Labour If the cuts are necessary, where's Philip Hammond's deficit target gone?