One of the biggest obstacles to a Labour victory at the next election remains the lack of economic trust in the party. Three years after David Cameron and George Osborne entered office, it is still blamed more for the spending cuts than the coalition (owing to "the mess" it left in 2010) and viewed as fiscally irresponsible. With Labour likely to pledge to invest significantly more than the coalition in housing and other infrastructure projects (while abiding by George Osborne's day-to-day spending totals), it is politically vital to shift this perception.
That is the task that Ed Balls has set himself for his speech today in which he will announce that he has asked the Office for Budget Responsibility to audit every tax and spending pledge in Labour's election manifesto. Balls will say:
In tough times it's even more important that all our policies and commitments are properly costed and funded.
The British people rightly want to know that the sums add up. So we will go one step further and ask the independent Office for Budget Responsibility – the watchdog set up by this government – to independently audit the costings of every individual spending and tax measure in Labour's manifesto at the next election.
This is the first time a Shadow Chancellor - the first time any political party in Britain - has ever said it wants this kind of independent audit. A radical change from what's gone before, but the right thing to do to help restore trust in politics.
It's a smart move that provides Ed Miliband with some political cover ahead of his speech tomorrow, which is likely to include major spending commitments on housing. But, crucially, Balls's plan would require an extension of the OBR's remit, which does not currently allow it to scrutinise the opposition's fiscal policies. Any change to this would require the approval of parliament, with number-cruncher-in-chief Robert Chote emphasising that a "cross-party consensus" is "highly desirable".
But just 17 minutes after Balls's announcement, the Tories put paid to any hope of securing one, with Sajid Javid, the increasingly prominent Economic Secretary to the Treasury, declaring:
Ed Balls knows this is not allowed under the Budget Responsibility Act and the OBR's charter, so this is just a stunt to try and distract attention from the fact that Labour have been found out for making unfunded commitments that would just mean more borrowing and more debt.
Nothing has changed - it's the same old Labour. Ed Miliband and Ed Balls still want more spending, more borrowing, and more debt - exactly how they got us into this mess in the first place. And it's hardworking people who would pay the price through higher taxes and higher mortgage rate.
The Tories' decision to torpedo Balls's plan is entirely politically motivated. There is no reason in principle why they should refuse to allow the watchdog founded by Osborne in 2010 to audit Labour's policies. But there are plenty of political ones. The Tories are understandably reluctant to allow Labour to enhance its fiscal credibility and to repeal claims of a "black hole" in its plans.
Tonight, Balls's SpAd Alex Belardinelli has rightly responded by asking how the Tories intend to justify their opposition to the proposal.
Surprising & disappointing that the Tories are not backing our suggestion to enhance role of OBR - why won't they support it?
— Alex Belardinelli (@abelardinelli) September 22, 2013 
It will be worth watching to see how Osborne's team respond when independent figures, dedicated to encouraging evidence-based policy, deplore their cynicism.