Debt interest is now a first-order Budget line

The Autumn Budget of 2025 did the thing British Budgets now do: it raised the tax take as a share of GDP toward a post-war high, announced that this was responsibility, and left the gilt market to pass its own verdict on whether responsibility had been bought or merely described. Bank Rate at 3.75 per cent is not an emergency rate. It is a rate at which a large public debt stock, rolled over on a calendar the Treasury does not control, becomes a first-order spending line. Debt interest is not a residual you squint at after the NHS and defence have had their go. It is a claimant that arrives before the argument starts.

For more than a decade the state became used to a world in which the Bank of England’s balance sheet and a collapsed real rate conspired to make borrowing look cheap. That world has gone. The Debt Management Office still does its job with the professionalism the rest of Whitehall likes to borrow in speeches. It cannot repeal arithmetic. A 25 basis-point move in Bank Rate, or a 25 basis-point move in the gilt curve that anticipates one, is a Budget event. Treating it as a market mood is how you walk into a mini-Budget without calling it that.

Rules that ignore the refinancing calendar are theatre

Fiscal rules in Britain have a half-life slightly longer than a reshuffle and slightly shorter than a parliament. They are useful when they constrain a Chancellor who wants to be constrained. They are decorative when they are written around the measure that happens to be behaving. A rule that targets a current deficit while the debt-interest line is being set in Threadneedle Street and in the Middle East is a rule that has chosen its battlefield for comfort.

The gilt market is not a mood. It is the price of a refinancing calendar.

There is a grown-up version of this. Publish the refinancing profile in language a non-specialist can read. Show, in the same table, the sensitivity of debt interest to Bank Rate and to a 50 basis-point steepening. Stop describing investment as if it were a luxury the gilt market will always fund at the previous decade’s rate. If the state wants a capital budget that survives contact with 3.75 per cent money, it has to pick projects whose social return clears that hurdle, not projects whose press return clears a weekend.

Tax take is not the same as tax capacity

Raising the share of GDP taken in tax is possible. It has just been done. Raising it while housing is lightly charged, while inactivity sits at 20.9 per cent, and while productivity — even on the cheerful measure — grows at 1 per cent, is a decision to keep asking the same workers and the same consumption base for more. That is not automatically wrong. It is automatically finite.

The essay on housing in this issue is the pair to this one. A property-tax reform that recasts council tax and stamp duty would be a fiscal reform, not a local-government curiosity. A labour-supply reform that treats NHS waiting times as a participation instrument would be a fiscal reform, not a health-service curiosity. Until those arrive, the Budget will keep doing what it did in 2025: lift rates on the bases that are easy to find, and hope the gilt market remains polite. Politeness is not a policy. It is a price.

This essay is commentary, not advice. Sources: Bank of England, Office for National Statistics, House of Commons Library, Office for Budget Responsibility, Resolution Foundation. See the editorial method.