In the previous chapter, we saw that the evolution of policy in the early postwar period is best characterised as ‘fitful’. In particular, I identified a continual and evolving struggle for survival between competing and conflicting conceptions of government strategy. In this chapter, the aim is to develop this empirical observation theoretically by interrogating the main evolutionary mechanisms which contributed to the lack of continuity in public policy. Building upon the evolutionary schema outlined in Chapter Four, I will look at: the major environmental pressures that were brought to bear upon the implementation of policy; the subjective responses to these by the main actors of the period; and the processes of political learning that stemmed from such factors. Overall, I will argue that the overwhelming conflictual pressures placed upon governments in the postwar period created an environment in which two distinct evolutionary trajectories emerged: a progressive tendency towards state expansion, and an accompanying, but no less visible, tendency towards retrenchment. The outcome of these distinct policy evolutions, as we have seen, was a continual oscillation in government strategy between Keynesian expansion and liberal retreat, an oscillation which seriously hampered the ability of successive governments to learn how to deal effectively with Britain’s accelerating economic decline.