Exclusive: Fiscal watchdog predicts productivity downgrade will leave chancellor with £20bn gap to fill in budget

Too many want to do Britain down – Labour will defy the doomsayers and beat the forecasts

Rachel Reeves has said Britain can defy gloomy economic forecasts after the fiscal watchdog infuriated ministers by predicting a productivity downgrade would leave her with a £20bn gap to fill in her forthcoming budget.

The chancellor said she was “determined not to simply accept the forecasts” – which increase the likelihood she will break a key Labour manifesto pledge not to raise income tax – but would instead prove the predictions wrong.

Writing in the Guardian, Reeves acknowledged her decisions at next month’s budget “don’t come for free and they are not easy”, after this newspaper revealed she is considering the tax hike to help reduce a multibillion-pound shortfall.