With 14 days to polling day, David Cameron will seek to rally Tory supporters with a warning that they have two weeks to save Britains economy from an SNP\/Miliband nightmare. Chancellor George Osborne told The Daily Telegraph that a Treasury analysis had calculated that the SNP would add £6 billion to Britains debt interest payments. He said: Theres a real cost for families of that. Its equivalent to just over £350 per family. Ed Miliband will respond with a warning of his own that the scale of the cuts planned by the Conservatives for the first half of the new parliament is unprecedented in any three-year period since demobilisation at the end of the Second World War. He will tell a rally in Leeds that figures from that International Monetary Fund (IMF) show that they are greater than anywhere else among the worlds 33 advance economies. The exchanges come as the independent experts at the Institute for Fiscal Studies prepare to deliver their analysis of the spending plans of the two main parties as well as the Liberal Democrats and the SNP. Mr Cameron will say: Weve learnt from the polls that every vote is crucial. We need just 23 seats to stop the SNP\/Miliband nightmare - one that would hit everyone in the pocket. Weve got just two weeks to make our case: the case for a stronger economy and brighter future for Britain. Nothing less than the future of your family depends upon it. Mr Miliband will say that Mr Camerons promise of a return to the good life under the Conservatives was a grand deception: The Tories are committed to the most extreme spending plans of any political party in generations. It is a plan so extreme that far from protecting the NHS they would end up cutting the NHS. It is a plan so extreme that it wouldnt mean three years of the good life, it would mean three years of hard times.