Labour were keen to make a big deal out of their manifesto being fully funded and costed when it was released on Monday. And Labour staffers were proud that the Tories weren’t able to pick any holes in the costings either. No-one was prouder of this than Ed Balls – especially when the Tories committed themselves to tens of billions of unfunded spending pledges.

And now he’s going on the offensive.

Tomorrow Balls will publish an audit of spending and tax commitments in the Tory manifesto arguing that it contains £25 billion a year of unfunded and unexplained promises. In what looks certain to be described as a “bombshell”, he’ll say that this is £1,439 a year for every working household in Britain.

The Shadow Chancellor will also take the opportunity to call (again) for legislation requiring the Office for Budget Responsibility to independently audit manifesto spending and tax commitments in all future elections.

Balls will frame the choice as being between”real, concrete, fully-funded pledges from Labour or fantasy and unbelievable promises from the Tories” – as well as arguing that the cost for Tory pledges won’t fall on “those with the broadest shoulders”:

“So who will pay the price of these £25 billion of promises which the Tories can’t say how they will pay for?David Cameron and George Osborne say ‘look at our track record’. And their track record shows it won’t be those with the broadest shoulders who will be asked to make a bigger contribution. Just look at how they have given a huge tax cut to millionaires, opposed Labour’s mansion tax for the NHS and refused to repeat the bank bonus tax. Just look at how they have given a huge tax cut to millionaires, opposed Labour’s mansion tax for the NHS and refused to repeat the bank bonus tax.”