The UK government website has basic facts on National Insurance system and its categories.
Taxaid charity has basic understandable guides for citizens.
on 10th March 2017. Fact checking organisation fullfact examined economic cliams about the impact of changes to the NI rates
Why was the change necessary? what was the reaction to the original budget?
See comment on the original NI changes from a number of newspapers and pre4sure groups
Tax Payers Alliance
Federation of Small Businesses
Institute of Directors
Research on UK tax reform.
Adam Smith (Free Market think tank)