Employees generally pay higher NICs than the self-employed unless they are very low paid. This is because Class 2 NICs are currently charged at a flat rate of £3.05 per week (2021-2 figures)
If you are self-employed, you pay two classes of NICs – Class 2 and Class 4. There’s a really good guide to how all of this works over at the Low Income Tax Reform website – here.