The official forecaster has been conducting an evaluation of productivity growth during the Tory years of government and has concluded that its assumptions about future productivity growth – that is output per hour worked – are too optimistic. That requires £20 billion of tax rises. There is zero chance of spending reductions being found to cover the shortfall so a very significant £30 billion of tax increases are needed. The nightmare for the chancellor and prime minister is they will be blamed for the inevitable tax rises. As government sources said to me, it will be hard enough identifying £30 billion of tax rises that don’t weigh too heavily on growth, without breaching manifesto pledges not to increase income tax, national insurance, VAT or corporation tax.