The OBR & fiscal rules

Twice a year, around the Budget and an autumn statement, a single document can reshape British politics: the forecast from the Office for Budget Responsibility. A few tenths of a percentage point in its growth projection can hand a Chancellor billions of pounds of room to manoeuvre, or wipe it out. Yet the OBR is barely a teenager as an institution, created in 2010, and the “fiscal rules” it polices are not laws of economics but choices governments make about how to constrain themselves. Understanding both is essential to making sense of any modern Budget.

What the OBR is, and is not

The Office for Budget Responsibility is the UK’s independent fiscal watchdog. Its core job is to produce the official forecasts for the economy and the public finances that underpin the government’s tax and spending plans. It also assesses whether the government is on track to meet its own fiscal rules, and it scrutinises the costings of individual tax and spending measures to check they are reasonable.

Crucially, the OBR does not make policy. It does not decide how much to tax or where to spend — those are decisions for the elected government, and ultimately for Parliament. The OBR’s role is to forecast the consequences of the policies the government has chosen and to judge them against the stated rules. It informs the debate; it does not settle it. Keeping this line clear matters, because the OBR’s authority rests precisely on its being seen as impartial rather than as a player in political choices.

Why hand forecasting to an independent body at all? The answer lies in a temptation. Before the OBR existed, the Treasury produced the government’s own economic and fiscal forecasts. That created an obvious incentive: a government wanting to make its borrowing plans look affordable could lean towards optimistic assumptions about growth or tax receipts. Independent forecasting is designed to remove that temptation and to give voters and financial markets numbers they can trust.

What fiscal rules are

Fiscal rules are self-imposed numerical constraints that a government sets for its own budget. Rather than being imposed from outside, they are commitments a government makes about how it will manage borrowing and debt over a defined period. Typical rules target getting debt falling as a share of GDP by a certain point, limiting day-to-day borrowing, restricting borrowing to investment, or capping the deficit. The precise rules change from government to government — they have been rewritten many times — but they almost always focus on borrowing and the debt-to-GDP ratio over a rolling horizon of a few years.

Governments adopt such rules for reasons of credibility and discipline. A clear, public commitment to control debt is meant to reassure both voters and the lenders who buy government bonds. If markets believe a government will keep borrowing sustainable, they are more willing to lend at lower interest rates, which lowers the cost of servicing the debt. Rules also impose discipline internally, giving a Chancellor a line to hold against spending demands from colleagues. They are, in effect, a way of tying one’s own hands to make a promise believable.

Headroom, costings and the Budget process

In the run-up to a Budget, the OBR prepares its economic and fiscal forecast, working alongside the Treasury to cost the measures the Chancellor intends to announce. When the government proposes a tax change or new spending, the OBR reviews the Treasury’s estimate of its cost or revenue and certifies whether it is plausible — a guard against measures being sold with implausibly flattering price tags. On Budget day the OBR publishes its forecast and its verdict on whether the fiscal rules are met, anchoring the figures the Chancellor stands up to present.

This is where the much-discussed idea of “headroom” enters. Headroom is the margin by which the government is forecast to meet its rules — the spare room to spend more or cut taxes without breaking them. Because that margin depends on uncertain projections of growth, inflation, interest rates and productivity, small revisions in the OBR’s forecast can create or destroy billions of pounds of headroom from one forecast to the next. A Chancellor can find their room for manoeuvre transformed not by any decision of their own but by a modest change in the watchdog’s assumptions.

The limits of rules

Fiscal rules are not without critics, and the criticisms are worth taking seriously in a non-partisan way. Because the rules are self-imposed, they can be rewritten when they become inconvenient, which erodes the very credibility they are meant to provide. Rolling targets, typically judged a few years out, can be gamed by promising painful adjustments in the future that never quite arrive. And rigid rules can push governments into poor decisions, such as cutting valuable long-term investment to hit a near-term debt target, or constraining borrowing during a genuine emergency like a pandemic or financial crisis when extra spending may be sensible.

The underlying tension is between discipline and flexibility. Rules firm enough to be credible may be too rigid to cope with shocks; rules flexible enough to absorb shocks may be too soft to reassure anyone. Designing rules that strike this balance — and an independent watchdog respected enough to hold a government to them — remains one of the enduring puzzles of fiscal policy, in Britain as elsewhere.