Were the Tories’ dodgy figures designed to provoke Labour into making a statement?

Why are the Tories peddling what the independent Institute for Fiscal Studies has described as ‘at best unhelpful’, which is the claim that households would be hit with a £3,000 tax bombshell if Ed Miliband becomes Prime Minister? The IFS’ analysis came out earlier today, but this evening George Osborne repeated the claim, saying:

‘Well it’s based on what the Labour party has voted for and what Ed Miliband has said he will do… I am confident that that is based on what the Labour party has voted for in Parliament.’