You set up an umbrella company with yourself as a shareholder
You pay yourself minimum wage, thus paying little income tax and national insurance
You then pay yourself and any other shareholders a dividend based on profits but this is taxed at a much lower rate than employee income and without national insurance
Advanced players set up their umbrella company in another country where the company taxes are even lower
Personally I think all tax breaks businesses get should be available to individuals; corporations have long campaigned for the rights of the individual like liable and so on with a fraction of the tax burden, surely it should be available the other way around. Particularly when it comes to paying any tax if you haven’t earned enough to feed and house yourself.
Looking at it another way: companies pay tax on profits, we pay it on revenue.
But that hasn't been the situation for quite a few years now so the financial arguments to "justify" IR35 don't really make much sense any more.