Sir Anthony Seldon (HS 67-72) is the doyen of Prime Ministerial history – having written definitive accounts of the last five occupants of Number 10. His new book, 'The Impossible Office', marks the third centenary of the office of Prime Minister, and explores how and why it has endured longer than any other democratic political office in world history.

From Robert Walpole and William Pitt the Younger, to Clement Attlee and Margaret Thatcher, Seldon discusses which of our Prime Ministers have been most effective and why. He reveals the changing relationship between the Monarchy and the office of the Prime Minister in intimate detail, describing how the increasing power of the Prime Minister in becoming leader of Britain coincided with the steadily falling influence of the Monarchy.

He begins the book with an imagined conversation between Sir Robert Walpole, the first holder of the office, and Boris Johnson. "I nearly died in my first year too," Walpole tells his fellow Etonian over a glass of Château Lafite. "Carteret – bastard! – was priming himself to take over." Three hundred years might separate Walpole and Johnson but there are many similarities. Besides both nearly dying in their first year in office, both were King’s Scholars at Eton, both boarded in Long Chamber, both came to office making the best of opportunities – the South Sea Bubble and Brexit – and both were involved with women more than 20 years their junior.

Seldon later has innocent fun ranking PMs, much how cricket fans sometimes amuse themselves compiling fantasy World XIs. Among "agenda changers" he picks Pitt the Younger alongside Walpole, Peel, Palmerston, Gladstone, Lloyd George, Attlee and Thatcher. Further categories include "major contributors" (Churchill and Blair make this group), "positive stabilisers" (Salisbury, Macdonald, Major, Brown, Cameron), "noble failures" (North, Chamberlain, May), "ignoble failures" (the "louche" Melbourne, poor Eden and Rosebery, who "lacked gravitas"). The final group, "left on the starting block", is for the 11 PMs who lasted less than 16 months.

The book celebrates the humanity and frailty, work and achievement, of the 55 remarkable individuals that averted revolution and civil war, leading the country through times of peace, crisis and war. For more fascinating insights into Prime Ministerial history, be sure to get yourself a copy.