This is my very basic understanding of what has happened. Would be happy, delighted even, to be corrected with what I've misunderstood.
Yes the policies are traditionally 'stress tested' by the OBR in terms of social impact etc.
However, ThickLizzie and KK decide "Fuck that .... we'll listen to our disaster capitalist mates ... and do what they want ...." Once that decision was made, it is alleged they then told hedge funds their plan in advance of sharing the lunacy with the electorate. Meanwhile, their mates and now the hedgefund managers set about shorting the £, making £Bs for themselves in the process.
I heard the ex-governer of the BoE yesterday saying (obviously paraphrasing here) .... The BoE has its foot on the brake in a tried and tested way of attempting to reduce inflation. TL/KK/their disaster capitalist mates have their foot full on the accelelartor in an attempt to crash the economy (whilst syphoning off as much as possible for their mates).
So far as I understand it, beyond 'helping out' their mates, they intend (now as a result of their reckless spending/borrowing) now to reduce the state - NHS, education, welfare - just about everything that matters to ordinary people.
Meanwhile, tonight, the IMF have confirmed the UK is an economic basketcase and we're circling the drain towards banana-republic territory.