At the halfway mark of Parliament, with the Government's economic targets essentially unreachable, is this the day Osborne pivots from Plan A?
The 4G messaround has revealed that the OBR has exactly the same problems that the American CBO – on which it was modelled – has; namely that it has to take whatever assumptions the politicians asking it to forecast give them.
In the US, that means Paul Ryan gets the CBO to confirm that his plan reduces borrowing by telling them, essentially "please take note that on page 4 I've said I will reduce borrowing." And in the UK it means that the OBR will look at the "size of the deficit" but allow Osborne to decide what constitutes the deficit.