This article discusses the implications of the decline of National Insurance in Britain, witnessed by its declining share of social security spending and steady dilution of the ‘contributory principle’ on which it was originally based. This decline is not accidental: under governments of the Left, arguments for inclusion have predominated, non-contributory benefits expanded and contribution conditions softened; under those of the Right, limited resources have been focused on the poorest through means-testing. From this starting point, the strong arguments in principle for social insurance look much weaker. However, there are also reasons why the system has not been swept away, notably the way in which most of it concerns already accrued state pension rights. The effect of current plans for state pensions is to restore something closer to a flat rate state pension, but with significant complexity. The article suggests a way in which a more transparent system could guarantee a total state pension at a fixed percentage of average earnings. Other National Insurance benefits could either be separated from pensions and absorbed within other working age social security, or the scope of National Insurance could be maintained, but based on a test of participation, not past contributions.