Britain’s public finances suffered an unexpectedly sharp deterioration in August, piling pressure on Chancellor John Healey ahead of his first Budget and narrowing the government’s room for manoeuvre on tax and spending.

Public-sector borrowing reached £18.3bn during the month, according to figures reported on 9 October. The result was the second-highest August total on record and exceeded the official forecast by £3.5bn.

The figures provide the clearest warning yet that rising debt-servicing costs and higher welfare and public-service spending are threatening the government’s fiscal plans. Borrowing accumulated between April and August reached £77.3bn, compared with an Office for Budget Responsibility forecast of £47.1bn.

Debt interest drives pressure

Central-government debt-interest payments climbed to £8.8bn in August, the highest figure recorded for the month. Inflation-linked government bonds were a major factor, as higher inflation increased the cost of servicing index-linked debt.

The deterioration comes as investors assess the scale of the government’s borrowing requirement. Bank estimates suggest net gilt issuance in the next financial year could reach a record level, while the Debt Management Office projects gross financing of almost £1tn over the next four fiscal years.

Higher borrowing needs could push up gilt yields if markets demand additional compensation to absorb the supply. NatWest Markets has forecast that 10-year gilt yields could reach 4.3% by the second half of next year, according to reporting cited on 9 October.

Budget headroom under strain

The data leave the Chancellor facing difficult choices before the 28 October Budget. A larger deficit reduces the scope for tax cuts or new spending unless the government raises revenue, restrains expenditure or accepts a weaker fiscal buffer.

Emma Reynolds, the Chief Secretary to the Treasury, said the government remained committed to fiscal discipline and would maintain protection against uncertainty. However, the scale of the overshoot is likely to intensify scrutiny of the government’s commitment to its fiscal rules.

The borrowing figures also arrive against a fragile economic backdrop. Business activity has slowed, with the S&P Global flash composite purchasing managers’ index falling to 51.7 in September from 52.5 in August. The survey indicated quarterly growth of only about 0.1%, while rising energy and fuel costs pushed input-price inflation higher.

Markets and businesses watch closely

For financial markets, the combination of weaker growth, elevated inflation and heavier government borrowing presents a difficult mix. Higher gilt yields would increase the cost of new borrowing and could feed through to mortgage rates and corporate financing costs.

Businesses are also awaiting the government’s response. The Chancellor has announced a £150m fund for fast-growing northern firms, with the British Business Bank expected to invest between £5m and £15m per company in innovative businesses and university spin-outs. Yet the initiative faces questions over whether it will materially improve growth while the wider economy remains constrained.

The immediate challenge for the Treasury is to restore confidence without further weakening demand. The August borrowing figures make that balancing act considerably harder and place fiscal credibility at the centre of the October Budget.