The election campaign has hit its paradox moment. Vote Tory for reckless, unfunded public spending. Vote Labour for extreme fiscal responsibility. This week’s manifestos, starting with Labour today, cannot be taken at face value. They are opening bids for the manifesto that dares not speak its name, the outcome of post-election coalition treaties, winks and nods. But the noise is important, the tone of voice, the mentions and the silences.

From the moment last week when the Tories were panicked on the NHS and promised to fill its “funding gap” with £8bn from nowhere, the invitation was there for Labour to retaliate. It has done so, with a pledge of no unfunded promises: “Every policy in this manifesto is paid for without a single penny of extra borrowing.”

It seems hardly decent to pick apart such language. Labour’s more-nurses pledge was once paid for by a mansion tax. It is now paid for by a mansion tax plus a tobacco levy. More child care is paid for by a bank levy. Smaller class sizes are paid for by no more free schools. Question any figure and the gap is met by “efficiency savings”. So too are more Trident submarines, lower student fees, more police, more railways and more houses. It is all just promises.

The one serious innovation, yet to be tested, is to subject such policies to a fiscal lock, audited by the Office for Budget Responsibility. Each must be paid for specifically, ensuring none of them increases the budget burden. This is a technical advance on the Tories’ weaker “charter for budget responsibility” proposed in January.

What is not clear is if it allows a future Labour chancellor to get off a manifesto hook by simply saying the OBR has refused to “certificate” a new policy as not increasing the deficit. It also leaves open the treatment of normal welfare spending unrelated to these election promises. Can borrowing rise for benefits and pensions, or will they be “locked” too? And what of the Tory accusation that Labour’s plan is £30bn adrift of fiscal balance over the next parliament?

The good news is that this bout of “rival fiscal responsibility” suggests a more mature approach to public finances. The impact on the campaign remains to be seen. Clearly the Tory charge that Labour and its leader, Ed Miliband, were not to be trusted on spending and borrowing has hit home. Labour’s manifesto is an in-your-face rebuttal. Miliband has at least got the point. And no one even dares to breathe the word austerity.