The office, Plumb indicated, was created out of the blue in 18^th century England. The realisation that they now had a prime minister came as an unpleasant surprise to many observers at the time.

Of course in 1965 I never actually sat in on the Ford Lectures. My exposure to Jack Plumb's wisdom was circuitous.

In 1967 Professor Plumb converted his lectures into a book. It was called The growth of political stability in England: 1675-1725.

In 1968 The Canberra Times commissioned a review of Plumb's book. It asked a lecturer at the Australian National University named David Johanson to write about it. His review was published (June 15) and he also devoted one of his lectures to the book.

1968 was supposed, then and now, to be a year of revolutionary ardour but Plumb's focus, Johanson pointed out, was different. It was on the countervailing force of anti-revolution.

The learned British historian plumbed the orderliness that settled on England in the decade after the installation of the House of Hanover in 1714. Such an act of anti-revolution was an unprecedented phenomenon. Chaos had been the norm in England since the death of Elizabeth I in 1603. Rebellion and revolution interspersed with mass hysteria and treachery had prevailed for much of the 17th century.

Plumb, Johanson told us, portrayed the emergence of political stability after 1714 in terms of three big developments. All were, incidentally, things that a Canberra audience was familiar with: a shameproof party system; much firmer executive control over the elected legislature; and the establishment of a network of like-minded public and political figures.

Creation of the office of prime minister stitched Plumb's three great strands together.

The office was established in 1721 specifically to deal with the so-called South Sea Bubble which was Hanoverian England's version of the GFC. The first occupant was Sir Robert Walpole.

Walpole thereafter did everything to entrench his novel position. He began by debauching the two party system of his day. The prime minister marginalised and discredited firmly principled people in both the Whig and Tory parties. Zealotry was equated with instability, now a seriously dirty word.

After 1721, with Prime Minister Walpole in the ascendancy, the executive wing of the government in Britain commanded an utterly reliable majority in the House of Commons. Such a thing had not happened since the Tudors.

Patronage perpetuated itself. Walpole and his sidekicks fully exploited the public sector funds and employment opportunities at the disposal of the crown. Access to seats in both chambers of parliament and to official positions of all kinds, including jobs in the army, navy, church and what passed for the civil service underpinned a vast network of dependency.

Walpole was the first person in British politics who was simultaneously the dominant figure by far in the House of Commons and the chief if not sole political adviser to the monarch.

For a few vocal observers the triumph of Walpole was scary stuff. Traditionally the people relied on by the monarch for political advice were seen as odious and creepy. But under Walpole, a dear friend of the royal court ran the House of Commons. Members of parliament were supposed to protect the nation against the monarch's invariably evil counsellors. This clearly no longer was happening.

The emergence of the office of prime minister bred fear. This anxiety bred a profusion of dystopian pamphlets and tracts culminating in Gulliver's Travels.

But it did not take long before these fears ebbed in England (although not in its American colonies). Acceptance of the new reality was symbolised by the fate of Gulliver's Travels which continued to be read, but only as a book for children. Their parents sensed that, under Walpole, their country had never been more peaceful and prosperous.

Back in 1965, when he gave the Ford Lectures, Jack Plumb assumed that the office of prime minister would forever be, as it had been for the previous 200 plus years, perched securely at the apex of British politics.

Plumb was a good historian but he was no infallible prophet. He did not live to witness our current darkening age of instability and disruption. His three great truths are now quite undone.

The party system in Britain in 2019 is no longer stable and stolid. The executive wing of government can no longer count on winning vital divisions in the House of Commons. And the supporting network of hangers on in public institutions and in the media that any government needs to have exercises far less sway at a time when populist resentment has been empowered by the resort to referenda on fundamental political issues, and with the election of party leaders by rank and file members who proudly do not subscribe to the wisdom prevailing at Westminster.

The template imposed in 1721 and which Jack Plumb described is in deep trouble. Prime Minister Boris Johnson, in the lead-up to the recent dissolution, was a grotesque shadow of his great predecessor Walpole. He did not command a meaningful majority in the House of Commons and vital advice to the monarch was overruled by legal action.

The year 2021 will mark the 300th anniversary of the invention of the office of prime minister of the United Kingdom. But will the office exist in any real sense by then if things continue as they are?