The main assumptions underlying these remarkable forecasts are entirely realistic: Saunders expects oil revenues to slump in exactly the same way as the OBR is predicting, that Scotland's share of total UK public spending will remain at 9.3pc and that non-oil GDP will continue to grow at the same rate as that of the rest of the UK. It is hard to see how anybody could really disagree, but the implications of his number-crunching are grim for the SNP.