It might surprise someone, who knew only On Liberty, to hear J. S. Mill called the father of British socialism. That would sound a careless bid for a respectable pedigree, on a par with hailing King Canute as father of the British seaside holiday. Mill is passionate there about making the individual a protected species, not to be interfered with even for his own good, unless to prevent harm to others. He is so passionate that government seems at times to have no other task than to protect. The Principles of Political Economy, on the other hand, displays clear, if intermittent, socialist leanings. There too ‘there is a circle round every individual human being, which no government… ought to be permitted to overstep’ (PPE V.xi.2, p. 306). But, subject to this constraint, government is urged to do all the utilitarian good it can and some nasty worries for democratic socialists surface instructively. They centre on the social aspects of individuality and give rise to problems in what my title calls the Social Liberty Game. British socialism, with its Lib-Lab origins and tolerant respect for individual liberty, embodies a tension between the rights of each and the good of all, which makes the Principles a living part of its intellectual history.