Britain’s response to political extremism is perhaps best encapsulated by PG Wodehouse’s fictional character, Roderick Spode, the 7th Earl of Sidcup.

Spode, or Lord Sidcup, is a recurring character in Wodehouse’s Jeeves novels and leads the fascist Saviours of Britain or the “black shorts”, as they’re popularly known.

“The trouble with you, Spode, is that just because you have succeeded in inducing a handful of half-wits to disfigure the London scene by going about in black shorts, you think you’re someone,” Bertie Wooster tells him on one occasion.

The character of Spode is, of course, Wodehouse’s none-too-subtle take-down of the British Union of Fascist leader Oswald Mosley.

It does nothing to detract from the thuggery and violence of Mosley’s blackshirts — and the resultant fear it produced, especially among London’s Jewish community in the 1930s — to admire the fact that, as a nation, Britain has more commonly laughed at and ridiculed, rather than voted for, the far right or the far left.

Even at its goose-stepping height, Mosley’s party never performed well at the ballot box.

On the one occasion it submitted itself to the voters’ judgment — the 1937 London County Council elections — the BUF failed to capture a single seat. Mosley’s attempted postwar comeback was similarly utterly unsuccessful.

It is true that Mosley’s far-right heirs — the National Front and the British National party — have, on occasion, managed to pull off local successes. The NF finished third in three parliamentary by-elections in the 1970s. In 2008-9, 100 BNP councillors were elected, and the party captured two seats on the Greater London Assembly and in the European Parliament.

But these have victories have always been short-lived and have never been translated into a national breakthrough: indeed, when Nick Griffin tried to unseat the redoubtable Margaret Hodge in Barking and Dagenham in 2010, she easily saw him off and overall the party polled a mere 1.9 per cent nationally.

The far-left — like its right-wing counterpart, often splintered between a host of parties — has been similarly unsuccessful at the polls. The Communists managed to elect four MPs in total, but by 1950 all were out of Parliament and the party has never managed to return another.

Since then, the far-left has only managed to get into the House of Commons when — as in the case of the likes of Dave Nellist and Terry Fields — it has infiltrated the Labour party and run candidates under its banner.

Successive Labour leaders have, moreover, attempted to police the boundaries between the party and the “outside left”. The latter — these “cliques and cults that have since Labour’s creation sought to use us as a cloak of respectability for their extremism and intolerance,” as the former Cabinet minister Alan Johnson put it at the weekend — was to be kept out of the party.

Thus in the late 1930s Clement Attlee — who later brought Britain both the National Health Service and Nato — refused the entreaties of those who wanted to form a Popular Front with the Communists and other radicals.

“Attlee knew that such unpatriotic opportunism would destroy the labour movement,” his biographer, John Bew, has suggested.

But when those boundaries were breached in the early 1980s, the taint of extremism and an ascendant hard left gave to the party was enough to keep Labour out of power for nearly two decades.

An important symbolic moment in Labour’s recovery came when Nellist and Fields were expelled in 1991 and deselected as parliamentary candidates for their membership of the Militant Tendency.

It took, however, Ed Miliband’s spectacularly ill-judged party reforms to change the equation. He threw Labour’s doors wide open and thus allowed virtually any militant, Trotskyite or Marxist who was happy to pay £3 the chance to pick the party’s next leader without even becoming a member.

Given that the best-placed far-left party — Nellist’s Trade Unionist and Socialist Coalition — polled just 0.1 per cent of the national vote in 2015, the opportunity to seize control of the Labour party was one the Trots were not going to pass up.

Under Jeremy Corbyn, Labour’s membership was transformed as moderates fled and were replaced by supporters of the new leader. While some at the top of the new Labour party — such as Momentum’s Jon Lansman — had been members for decades, many had not.

Andrew Murray, for instance, who ran the party’s 2017 campaign and became a key figure in Team Corbyn didn’t join the Labour party until late 2016, having just a year before proclaimed that “Communism still represents … a society worth working towards”.

On Mr Corbyn’s watch, Labour thus began to resemble one of the far-left parties it has always fought against. Its domestic agenda represented a throwback to 1970s-style state socialism. Its foreign policy was infused with the noxious New Left anti-imperialism of the Stop the War Coalition (in which both Corbyn and Murray had been leading lights).

And its internal culture — the veneer of internal democracy masking a sectarian, bullying and vicious form of machine politics — was familiar to anyone cognisant with Stalinist politics. The party’s political strategy, meanwhile, echoed the cry of the 1980s hard left: “No compromise with the electorate”.

Despite their doubts about Boris Johnson — the most unpopular new Prime Minister in four decades, according to the polls — voters reacted strongly to Labour’s mutation into a party of the far left last week, and the strongest reaction was registered by those who had once been its most loyal supporters.

Only those who previously represented the 0.1 per cent can have been surprised at such an outcome.