The Gig Economy and a shrinking Tax Base

An interesting aspect of the 2016 Autumn Statement is evidence that the UK tax base is shrinking as a result of the move towards the 'gig economy'.

I notice from this article I notice from this article that there's not much discussion of why - one of the implications is that the self-employed have less of an incentive to accurately report their incomes - and why would they, if they've got to fund medical care and pensions out of their meagre take home pay, rather than rely on their 'employers' meeting some of these costs.

However, it might also be the case that their incomes are lower - and thus fewer of them are eligible to pay tax in the first place. I'm a cynic - might the government be keen not to see this reported?