At the end of the day you can call it NI contributions or income tax but really it is just TAX…why have two names and two complex systems of collection & payment when you can have just one!!!
If you were to scrap national insurance contributions and increase income tax to compensate then you would greatly simplify the tax collection system for the HMRC. At a stroke this would cut in half the tax collection bureaucracy that exists in HMRC and the tax side of businesses as they would be dealing with one system (income tax) and the processes to deal with this are already in place.
This would reduce the amount of work and processes that accountants, employers, employees & HMRC had to perform.