UK Inflation Jumps to 3.5%: £24.5bn Borrowing Before Budget

UK consumer price inflation jumped to 3.5% in September 2025, up from 3.1% in August and above the 3.4% economists had forecast, according to the Office for National Statistics. The same data release showed public sector net borrowing reached £24.5 billion for the month, worse than expectations and the highest September figure in years, delivering a double blow to Chancellor John Healey just a week before the 28 October Budget.

What drove the September inflation rise?

The acceleration was driven mainly by motor fuel costs. Petrol rose 8.2p to 169.5p per litre and diesel to 192.5p, with fuel prices up 29.8% year on year after Middle East and European conflicts squeezed global oil supplies and disrupted flows through the Strait of Hormuz. Air fares, computer games and live events also added upward pressure, the ONS said.

The latest reading leaves inflation well above the Bank of England's 2% target and marks the highest rate in almost a year. The Bank of England interest rate decision next month is now in sharper focus, with markets increasingly pricing in a rise from the current 3.75% on 5 November.

How far did government borrowing overshoot?

Public sector net borrowing of £24.5bn was £1.8bn higher than September 2024 and £1.9bn above the Office for Budget Responsibility's monthly forecast. For the financial year to date, borrowing totalled £97.8bn, around £6bn above the OBR's projections. Debt interest payments hit a record £10.9bn for the month, partly because higher inflation lifts index-linked gilt costs, while total public sector debt provisionally exceeded £3 trillion for the first time, equal to about 94% of GDP.

Why is borrowing rising?

Higher inflation directly increases the cost of servicing index-linked government debt, while global energy shocks have raised departmental spending pressures. The UK public sector debt burden now constrains the Treasury's room for manoeuvre, economists note, because every additional percentage point of inflation adds billions to interest bills.

What does this mean for the 28 October Budget?

Chancellor John Healey must now set tax and spending plans with inflation accelerating and borrowing overshooting forecasts. He has promised to respect fiscal rules and Labour's pledge not to raise income tax, National Insurance or VAT. Healey blamed Middle East and European conflicts for the rise and said the Budget would be growth-focused. The Conservatives countered that Labour had lost control of the economy, while Capital Economics expects a cautious Budget with limited giveaways.

The figures also lock in higher welfare and business costs: benefits and business rates are uprated by 3.5% in line with September CPI, and the state pension is likely to rise 3.9% under the triple lock. That combination narrows the autumn Budget tax changes the chancellor can make without breaking his own borrowing rules.

Could interest rates rise next month?

With inflation at 3.5% and expected to climb towards 4% by early 2027, the Bank of England's Monetary Policy Committee faces a difficult call on 5 November. A quarter-point increase from 3.75% is seen as more likely than not, although some analysts argue the Budget's impact should be assessed first. The UK inflation forecast 2026 will depend heavily on energy prices and any further escalation in the Middle East.

Impact on households and markets

Households face higher petrol and diesel costs at the pump, while index-linked benefits and pensions will rise to offset part of the squeeze. Gilt yields moved higher after the data, reflecting reduced confidence in the fiscal outlook. The cost of living support measures in the Budget are now expected to be tightly targeted, rather than broad-based, to keep borrowing within the OBR's envelope.

FAQ: UK inflation and borrowing explained

What is UK CPI inflation?

The Consumer Prices Index measures the average change in prices paid by UK households for a basket of goods and services. A reading of 3.5% means prices rose 3.5% over the previous 12 months.

Why did UK inflation rise to 3.5% in September?

Higher motor fuel costs, up 29.8% year on year, were the main driver, alongside air fares, computer games and live events. Global oil supply disruption pushed petrol and diesel prices sharply higher.

How much did the UK government borrow in September 2025?

Public sector net borrowing reached £24.5 billion, £1.8 billion more than a year earlier and £1.9 billion above the OBR's monthly forecast.

What does higher inflation mean for the Budget?

It reduces the chancellor's fiscal headroom, raises debt interest costs, and forces up benefits and business rates, leaving less room for tax cuts or new spending.

Will the Bank of England raise interest rates?

Markets see a rate rise from 3.75% as possible at the 5 November meeting, especially if the Budget adds to demand pressures. The decision will depend on updated inflation and growth forecasts.

Conclusion

The September data create a difficult backdrop for the chancellor: inflation is accelerating, borrowing is overshooting, and debt has passed £3 trillion. The 28 October Budget will reveal whether the government can protect public services and investment while meeting its fiscal rules, or whether higher inflation and interest costs force a more restrained package than planned.