You pay National Insurance contributions (NICs) to build up your entitlement to certain social security benefits, including the State Pension. The type and level of NIC you pay depends on how much you earn and whether you're employed or self employed. You stop paying NICs when you reach State Pension age.

For more information visit - http://www.direct.gov.uk/en/MoneyTaxAndBenefits/Taxes/BeginnersGuideToTax/DG_4015904