You can pay voluntary NICs if you are low income, but it won't help you with PR status, they would not fulfil the CSI requirement.

Voluntary contributions may be required to ensure you get a full state pension, but you should get a pension forecast before making any payments.

If you are on a low income as a worker, the PAYE system will take care of your NICs. However, make sure you are paid properly through the company's books and NOT cash in hand.

NI contributions are not related to the NHS, they pay for things like state pensions and contributory, non means tested benefits, such as contribution based JSA and ESA.