This chapter offers a historical power analysis from the Saxons to the end of Pitt the Younger’s premiership. In the liminal premiership, the ‘key’ minister/advisor behind the monarch, or Oliver Cromwell during the republic, had serious power, but cannot be considered a prime minister as their power was wholly dependent on the monarch, and the complex machinations of court politics. The important innovation is how the role of ‘lead’ minister developed, with the monarch’s agreement, into the more independent ‘prime’ minister. We contend that only with Robert Walpole’s accession to the office did the power of prime minister become apparent, the primary reason being the monarch’s (George I) reliance on Walpole to control Parliament for spending and the protection of the monarch’s power. However, it was only with Pitt the Younger’s premiership, which truly established more formal parts of the office – particularly the Treasury, the state/economy and the Cabinet – that we see the beginnings of the modern office we know today.