The growing cost of pensions is set to help swell UK public debt to three times the size of the economy and will place ‘unsustainable’ pressure on the public finances, the budget watchdog has warned, days after Andy Burnham pledged to retain the expensive triple lock after taking power. In its annual report on the major fiscal risks facing the government, the Office for Budget Responsibility (OBR) revised up its public debt forecast in 2075 from 270 per cent as a share of GDP to 300 per cent. Public debt is hovering around 95 per cent, amounting to just under £3 trillion. [...]