To know the costs of manifesto promises, the OBR should be the first place we look

The Institute has previously argued the benefits of allowing the opposition parties to have their policies independently costed in advance of an election. At present, the rules of the game are tipped in favour of the government. The governing party (or parties) has access to civil servants and policy costings during their term. They can also ask officials to cost opposition party policies, albeit using their own assumptions: earlier this year the Conservatives published Treasury analysis suggesting that Labour’s manifesto contained £21bn of unfunded spending. A media spat ensued with Labour denying the claims, but with voters left little clearer on what the true cost of policies would be. The Office for Budget Responsibility (OBR) could help to remove such confusion and prevent pre-emptive policy costing for political gain. The OBR was set up in part to scrutinise the cost of government policies. It does not produce policy costings from scratch but publically endorses (or rejects) costings calculated by departments. At present, legislation precludes the OBR from considering non-governmental policies. If this were changed, the OBR could provide a similar level of scrutiny and an endorsement service for all policies, of government and opposition parties alike. There are numerous advantages to expanding the OBR’s role in this way. Civil servants already cost opposition party policies, with assumptions set down by Government special advisers. Under a reformed system, opposition parties could themselves submit policies to be costed by officials – using their own assumptions – and then have those costings certified by an organisation with no incentive to inflate or exaggerate costs. With more accurate costings voters could make more informed decisions: public debate could focus on the content of policies, rather than the accuracy of figures. To expand the OBR's role, the primary legislation governing it would need to be revised to allow it to consider non-government policy. Opposition parties would have to be granted access to government officials to submit policies, and precautions put in place to ensure these were not seen by ministers. Decisions would have to be made about when parties could access such a service, and whether they could use it to develop policies iteratively by submitting different versions of a policy to get a different cost. However, these barriers should not be exaggerated. Officials already cost opposition policies, albeit without input from the parties themselves. Opposition parties are already granted confidential access to departmental official during access talks, with the process successfully shielded from ministers. There is both civil service capacity to perform costings, and the confidential channels to allow exchange of information and policies to take place - but it is ultimately the politicians who must take responsibility for bringing clarity to this debate.