Thursday 3 April 1721 was an unremarkable day in political London. No fanfare or ceremony surrounded King George I’s appointment of Robert Walpole as First Lord of the Treasury (Prime Minister), merely a paragraph buried in the press: ‘We are informed that a Commiffion is preparing appointing Mr Walpole Firft Lord…’ Yet here was the start of what has become the longest-lasting head of government job in the democratic world — and its 300th anniversary falls on 3 April this year.