However, this keeping the debt share at sustainable levels would require a tightening of 1.9pc of GDP, or 0.4pc of GDP in each decade to 2065. "Tightening policy by 0.4 per cent of GDP a decade would see the debt ratio fall more slowly to begin with, but the overall tightening would be large enough to stabilise the debt ratio at around the target level and prevent it from taking off again," the OBR said.