Whilst IR35 itself is a tax law, in order to determine whether or not to apply IR35 you need to understand employment law and establish if you would be regarded as an employee of the end client in the absence of your limited company (often referred to as ‘disguised employment’).
Unfortunately, to make matters worse, employment law does not provide a distinction between employment and self-employment, leaving you to rely upon past judgments in common law to reach your decision.