Machinery of government arrangements attract a diverse and detailed literature, but surprisingly little comparative research. This article provides a graphically presented indication of functional changes in the architecture of national government in Australia, Canada and the United Kingdom between 1950 and 1997. An analysis finds interesting national differences, with sharp changes in practice in Australia and Canada, but more gradual incremental adjustment in the United Kingdom. The correlation between parties and machinery change is weak for Canada and the United Kingdom, but all countries demonstrate stronger links between elections, new prime ministers and machinery of government changes. Further, all tend to oscillate between many specialist departments and fewer, broader agencies.

The explanation for such machinery change, we argue, is found in the political, policy and administrative calculations made by prime ministers in Westminster‐style parliamentary systems.