The massive economic cost of the chancellor’s failure to commission the budget experts

In terms of unforced errors by the chancellor and prime minister, another big one was not to commission a fiscal and economic forecast from the independent Office for Budget Responsibility (OBR) in the mini-budget - because the lack of certainty around the likely impact of the tax cuts on the deficit and growth made the market reaction even worse than it would otherwise have been.

Or to put it another way, the inevitable fall in the value of sterling and rise in market interest rates were larger than they needed to be. The Treasury implied there was not enough time to commission the OBR. This turns out to be utter rubbish.

The OBR has confirmed in correspondence with Ian Blackford MP and Chair of the Treasury Select Committee Mel Stride that it told the chancellor it could deliver a set of forecasts up to the high standard demanded by the code it is legally obliged to follow.

But Kwasi Kwarteng chose not to take up the offer.

He decided to implement the unprecedented fiscal stimulus partially blind to the financial and economic consequences of what he was planning - while also depriving all of us of a robust independent assessment.

According to a government official, Kwarteng and Truss “were so set on what they were doing they just didn’t want any negative news that might have persuaded them to think again”.

It is very hard to see how they can restore confidence in their stewardship of the economy.

As The Guardian's Political Editor Pippa Crerar has revealed, they are meeting the OBR’s boss Richard Hughes tomorrow.

Perhaps he’ll give them some much needed tips.

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