Before deciding whether a policy is worth its cost, we need to know which cost is being discussed. A household saving, an annual Treasury bill and a total across several years can all describe the same policy. They aren't interchangeable numbers.
The coverage of electricity VAT and bus fares in July 2026 illustrated the problem. Different outlets presented a £45 household saving and an £850 million public cost for the electricity measure. Reporting of the bus cap used both £454 million and £500 million.
Those differences need explaining rather than automatically treating them as contradictions.
Ask what the number measures
A saving per household can be consistent with a large national cost. A tax cut can reduce a bill compared with what it would otherwise have been while the final bill still rises because other prices increase.
The comparison needs a period, a population and a baseline. Without those, readers can reasonably think two accounts disagree when they answer different questions.
Two different totals for what appears to be the same commitment raise another issue. They may reflect different assumptions or coverage, or one may be wrong. We shouldn't choose a winner without a published costing that lets us reconcile them.
The original bus-fare reporting belongs to that July announcement. Its figures shouldn't be mistaken for a fresh costing of policy today.
A useful convention
Every policy costing should explain whether it is per household or national, annual or cumulative, gross or net, and compared with what. The same explanation should survive into coverage when the number is repeated.
Headlines are short, and newsrooms often work from announcements that haven't supplied enough detail. Those are real constraints. They don't make the missing information unimportant.
People can reasonably disagree about spending several hundred million pounds on bus fares. That disagreement is much more useful if both sides know which sum, period and alternative they are weighing. Publishing a consistent costing won't settle the policy. It will let us have the argument about the policy rather than an argument about what the figures meant.