Your editorial ( The Guardian view on OBR v the Treasury: ministers have embraced the theatre of errors, 1 December ) correctly flags the huge uncertainty in trying to come up with a five-year forecast of the difference between taxes and spending. Although markets like big fiscal headroom numbers, they seem to ignore the wise words of Bertrand Russell, who defined mathematics as “the subject in which we never know what we are talking about, nor whether what we are saying is true”. This also applies to the concept of the medium-term fiscal headroom that economists and politicians alike are obsessed with.

Prof Costas Milas

University of Liverpool

The scrapping of the two-child benefit limit certainly seems to have polarised opinion. One camp reckons it should not have been scrapped at

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