However, we learnt last week that revenues for the first two months of this financial year were down by 3.4 per cent on the same period in 2013. Total current receipts were £92.3bn, versus £95.4bn in April/May last year. VAT receipts are fine, up 5.7 per cent, and that would square with strong consumption, and corporation tax is up too. But income tax and capital gains tax are down 4.7 per cent and National Insurance Contributions (NICs) are down 2.2 per cent. This is not what is supposed to happen, particularly since tax revenues have in the past been particularly strong in the early and middle stages of an economic recovery.

My thesis is that Macrae's second - grey economy - explanation is closest to the truth.

Perhaps the simplest determinant is whatever figures there may be enumerating the growth of working tax credit claims by newly self-employed people.

There are definitely safeguards - documented above - aimed at anyone reporting self-employed income at £11k pa or below, and my bet is that these safeguards are not currently being - and will not be until the election -  adequately applied.

"The future is already here -- it's just not very evenly distributed" William Gibson