Alistair Darling is hopeless at maths. Anthony Bolton is not good at shorting stocks. It’s hard to know which of this week’s revelations is the more surprising. Well, OK, it’s not that hard. But both should raise as many questions as eyebrows among private investors.

On Tuesday, the chancellor of the exchequer said he was extending the income tax personal allowance by £600 to provide a £120 tax rebate. At the same time, he said he was also “reducing the threshold at which an individual starts to pay tax at the higher rate by £600” – to ensure higher earners were no better off. But it didn’t take long for the sums not to add up. Reducing the higher rate tax threshold from the first £36,000 of taxable earnings to the first £35,400 doesn’t cancel out the £120 tax cut – because everyone’s taxable earnings have already come down by £600.