Re: I guess I misunderstood the situation
Define economy. EU has exclusive (in)competence in a lot of political and economic areas, not all of which serve UK economic interests. Brexit just means having UK hands on those levers, and less money flowing to the EU to bankroll EUrocrat's lifestyles.. Which can sometimes mean 'tax free'. It's odd that politicians often have favorable tax & expense treatment compared to us mere mortals.
I think IR35 is similary conflicted, with lobbying serving many interests, and the same with employment law in general. I guess a simplistic view starts with the contract. In my case, that's usually been pretty easy to define with design, implementation, commissioning and handover phases, often with seperate SoW and gaps between phases, which is the nature of that beast. It gets harder to argue when contractors are in post long-term, and not really attached to a defined project. But employers like that because contractors have fewer rights, and with some financial engineering, claim cost reductions.
But then the combination of IR35 and reduction in FTE benefits just means staff get screwed, and companies struggle to attract & retain staff, or find contractors willing to work on those terms. Which was probably what the big body shops wanted, ie hire them, or work for them, or don't work.