UK Borrowing Overshoot Puts Gilt Market at Centre of Budget Test

UK public sector borrowing overshot official forecasts again in August, sharpening the fiscal test facing Chancellor John Healey before the 28 October Budget and underscoring why gilt investors are focused less on year-on-year deficit improvement than on the government’s slippage against the Office for Budget Responsibility’s baseline.

The public sector borrowed £18.3 billion in August 2026, £2.9 billion more than in August 2025 and £3.5 billion above the OBR forecast. Borrowing in the financial year to August stood at £77.3 billion, £2.2 billion lower than in the same period last year but £8.1 billion above forecast. Public sector net debt was provisionally estimated at £2.9855 trillion at the end of August, equivalent to 93.8% of GDP.¹³

That distinction matters for fixed-income markets. A lower deficit than last year can point to some fiscal improvement. But an overshoot versus the OBR forecast threatens the assumptions underpinning gilt issuance, debt-interest projections and the Chancellor’s fiscal headroom. For investors, the key question is not whether borrowing is improving in isolation. It is whether the government is drifting from the path on which its tax, spending and debt rules were calibrated.

The borrowing number that matters is the forecast miss

August’s borrowing was the second-highest August on record in cash terms, behind only 2020, according to the ONS. The monthly deficit widened because spending growth outpaced the increase in receipts. Central government tax receipts rose by £2.5 billion from a year earlier, but total central government expenditure rose by £4.9 billion, including higher spending on goods and services, benefits and investment.¹³

The year-to-date picture is more nuanced. Borrowing in the first five months of the financial year was below the comparable period in 2025. At 2.5% of GDP, it was 0.2 percentage points lower than a year earlier. But the OBR comparison is more important for Budget arithmetic: the £8.1 billion overshoot in the financial year to August means the Chancellor enters the final month before the Budget with less confidence that the March forecast path remains intact.¹³

For gilt investors, that creates two risks. First, higher borrowing can imply heavier gilt supply than previously expected. Second, it can weaken confidence that the government can meet its fiscal rules without tax increases, spending restraint or both. That is why the market reaction to fiscal data often depends more on deviations from forecast than on the direction of travel versus last year.

Debt interest is now the fiscal constraint

The pressure point is debt service. Central government debt interest payable was £8.8 billion in August, the highest August figure since monthly records began in 1997, not adjusted for inflation. The ONS said £2.1 billion of that reflected the capital uplift on index-linked gilts, driven by recent Retail Prices Index movements.¹³

This matters because the UK’s debt stock is large, a material share of gilts is index-linked, and refinancing now occurs at much higher yields than during the ultra-low-rate decade. When inflation and gilt yields rise together, the Treasury faces a double hit: near-term index-linked debt costs rise, while future borrowing and refinancing become more expensive.

Political analysis ahead of the Budget has focused on the same constraint. Ben Zaranko argued in The Observer that multi-decade-high borrowing costs and higher debt interest leave Healey with limited room to avoid difficult tax choices, particularly if he wants to preserve market credibility.³ The Independent also reported that ministers have acknowledged a challenging Budget backdrop, with rising borrowing costs reducing fiscal flexibility.⁶

The Chancellor’s choices are constrained by the feedback loop between fiscal policy and gilt markets. A Budget that relies on optimistic growth assumptions, delayed savings or unfunded giveaways risks pushing yields higher. That, in turn, would worsen debt-interest projections and further erode headroom.

Market commentary has already linked sterling weakness and pressure in gilts to the August borrowing overshoot and higher debt-interest costs.⁷ A Telegraph report syndicated by Yahoo Finance separately noted that potential hits to fiscal headroom, including from weaker policy delivery elsewhere, come on top of pressure already created by higher borrowing costs and inflation.⁵

That dynamic makes the 28 October Budget less a conventional tax-and-spending event than a test of fiscal credibility. The Chancellor must show how the government will finance its priorities while keeping debt on a sustainable path and avoiding a gilt-market repricing that would make the fiscal position worse.

QT adds to the supply backdrop

The Bank of England’s quantitative tightening programme adds another layer to the gilt-market calculation. In a 28 September speech, Deputy Governor Dave Ramsden addressed QT’s role in the Bank’s balance-sheet normalisation process, a topic directly relevant to the amount of government debt the private market must absorb.²

QT is not fiscal policy, but it affects the market environment in which fiscal policy is executed. As the Bank reduces its gilt holdings, more duration risk sits with private investors. If government borrowing also comes in above forecast, the market must digest both ongoing issuance and the effects of balance-sheet reduction. That combination can increase the sensitivity of yields to fiscal news.

The practical consequence is that the Chancellor has less room to surprise investors. Even if the debt-to-GDP ratio is slightly lower than a year earlier, the cash debt stock remains close to £3 trillion and the marginal cost of financing is materially higher than in the pre-pandemic period.¹³

Growth pledges collide with fiscal arithmetic

Healey is trying to frame the Budget around growth and industrial renewal. The Treasury said on 28 September that the government would back British shipyards through major maritime projects, including three new floating docks for the Royal Navy’s submarine service and a new marine research vessel, as part of a “new age of industrialisation”.¹

The political logic is clear: investment in defence, infrastructure and industrial capacity can be presented as a supply-side growth strategy rather than simple current spending. The fiscal challenge is that markets still need to see how near-term commitments fit within the borrowing path. Growth measures may improve the long-run outlook, but gilt investors tend to price the near-term cash requirement and the credibility of the fiscal framework first.

The Independent’s coverage of Healey’s conference speech also noted that business groups were warning that renewed fiscal pressure and Budget uncertainty were weighing on activity.⁸ That creates a delicate balance. A Budget heavy on tax rises could dampen confidence; a Budget light on consolidation could unsettle gilts.

What to watch before 28 October

The next fiscal signal will be whether incoming data suggest August was a one-month deterioration or part of a broader drift from the OBR path. The ONS is due to publish the next public finances release on 21 October, one week before the Budget.¹³

For macro and fixed-income readers, three indicators matter most. The first is the cumulative borrowing gap versus the OBR forecast. The second is the path of debt-interest spending, especially the contribution from index-linked gilts. The third is the level and shape of the gilt curve, because higher long-dated yields feed directly into assumptions about future financing costs.

The August figures do not mean a fiscal crisis is imminent. Borrowing is still below last year’s level in the financial year to date, and debt as a share of GDP is lower than a year earlier. But the overshoot against forecast is the issue that will dominate gilt-market interpretation. It tells investors that the Chancellor’s room for error is shrinking before the Budget has even begun.