The only way to remove tax avoidance/efficiency is to radically simplify the system. All people pay x% tax on all *earnings*, and all companies pay y% tax on all *sales*. It would need a bit of work for expenses, but that should be fairly straightforward for both individuals and companies. Get it down from 600+ pages or whatever it is in the UK to under 20 and it would be a lot harder to game the system.
At the same time, make accountants equally liable for any dodgy schemes that people use. So if I was found to be doing something underhand and facing a large fine, the accountant would face exactly the same fine.