Yesterday I argued no one can accurately forecast the UK deficit or state borrowing for five years hence.The deficit is the difference between two much larger numbers, total spending and total income. If spending is £1.3 tn and income £1.2 tn the deficit is £100 bn. If the forecast is 5% too low on spending which is £65 bn then the deficit is £165 bn, or 65% higher.
The OBR has to make a whole series of assumptions about what will be happening in five years time. If they decide productivity disappoints, as they did for this budget, there is a bigger deficit to deal with. If they think interest rates will be higher, or tax revenues lower, again there is a bigger blackhole to fill. For this budget they upped the forecast of tax revenues so there was a forecast overall win, not a larger black hole.
Distracted by all this Chancellors spend time arguing over the assumptions which create big swings in requirements for extra taxes instead of concentrating on the much more important and real forecasts for the next financial year. The Treasury and OBR should be able to provide fairly accurate spending forecasts for next year. Chancellors should be pursuing proper controls over immediate spending.
The black hole in five years time approach can both lead to too many anti growth taxes and too little concentration on more immediate spending excesses. This last budget showed a Chancellor gaming the system with promises of tax rises to come and productivity gains in five years time to allow her to continue to spend and borrow too much for the rest of this Parliament.