The election manifestos are a missed opportunity. The Labour Party has gone to great lengths to tell us how its package of measures is fiscally neutral, but has said very little about the overall envelope for spending in the next parliament. The Conservatives have said they’ll run a budget surplus, but to meet that objective and honour the pledges they’ve made, spending on public services will probably have to be cut by more than they admit. A hung parliament now seems inevitable.

The parties like to tell you about the good but not the bad; about the spending but not the borrowing; the detail of the tax cuts but not the specifics of the cuts to public services. The Resolution Foundation aptly calls this the candour deficit. It’s reasonable to ask whether the independent Office for Budget Responsibility could play an assertive role in closing it. The OBR was told by the last government not to audit the election manifestos. That should change.

First, the numbers for individual policy measures would be confirmed free of wishful thinking. Second, and perhaps more importantly, voters would know more about the bits that will hurt as well as those that feel good. The OBR has already established a reputation for transparency – the manifestos would benefit from this treatment.

Indeed, the involvement of the OBR in vetting the manifestos has the potential not just to ensure the opposition’s policies are fairly costed, but also to lift the quality of the end product. It’s good when measures are dropped if they look too expensive or damaging once the details have been fleshed out. If the opposition had access to the machinery needed to develop its policies, voters could be more confident of their eventual implementation. That would level the electoral playing field and benefit the democratic process.

To perform this role the OBR’s function would need to change. But by far the biggest adjustment would be that required of the civil service. This poses some tricky challenges. How, for example, will opposition policies be developed in confidence when special advisers mix with civil servants in policymaking departments?

Now is the time to think about the practicalities – this should be a priority of the next government, whoever comes to power. Getting the OBR more involved will allow voters to make a better, more rounded assessment of fiscal plans and elevate the political discourse. It will benefit democracy.