UK Government debt is on an "unsustainable path" unless spending is tightened and taxes are raised, the independent forecaster has warned.
The Office for Budget Responsibility (OBR) said soaring energy prices and pressures from an ageing population risked tipping the UK into a recession.
Moving away from fossil-fuel vehicles to electric ones could also hit tax revenues, the OBR said.
Debt is the total amount of money owed by the government that has built up over years. In May 2022, it was £2.36 trillion. The figure almost exceeds the size of the UK economy, with debt having reached 95.8% of gross domestic product (GDP).
The OBR said the Ukraine war, soaring energy prices and long-term pressure on the nation's finances "add up to a challenging outlook for this and future governments as they steer the public finances through inevitable future shocks".
"Many threats remain, with rising inflation potentially tipping the economy into recession, continued uncertainty about our future trading relationship with the EU, a resurgence in Covid cases, a changing global climate, and rising interest rates all continuing to hang over the fiscal outlook," it said.
Households are currently being hit by higher fuel, food and energy costs. Prices are rising at their fastest rate for 40 years, with inflation at 9.1%.
The OBR said bringing debt back to 75% of GDP, the level at which it stabilised in the Government's pre-pandemic March 2020 Budget, "would need taxes to rise, spending to fall, or a combination of both".
"The pressures of an ageing population on spending and the loss of existing motoring taxes in a decarbonising economy leaves public debt on an unsustainable path in the long term," the OBR said.
The Government has pledged to ban the sale of new petrol and diesel-powered cars from 2030. Fuel duties are currently a big source of tax revenue.