The Office for Budget Responsibility (OBR), the government's independent economic forecaster, has warned that UK public debt is on course to rise unsustainably in the coming decades unless policymakers act soon. Driven by an ageing population, rising health and pension costs, and higher defence spending, the OBR projects that without government action debt would embark on an "unsustainable, ever-upward path from around the 2040s". The warning matters because it sets out the scale of the fiscal challenge facing the chancellor, Rachel Reeves, and points to difficult choices on spending and taxation.

In its latest fiscal risks and sustainability report, the OBR notes that defence spending would need to rise by an extra £28bn a year to meet the pledge to spend 3.5% of GDP. State pension spending could climb from 5% to 9% of GDP over 50 years — a third of that due to the triple lock — while health spending could rise from 8% to 13% of GDP by 2075. Although Reeves's plans are expected to stabilise the debt-to-GDP ratio at around 95% by 2030-31, the OBR expects it to accelerate again from the mid-2030s. Official Tom Josephs stressed that acting earlier would be far less costly than delaying. The OBR has lacked a permanent director since Richard Hughes resigned last December.