More than three years after a knife-edge public vote, a hung parliament seethes with talk of “plots”, “coups” and “conspiracies”. Protestors march on Westminster, demanding the resignation of the government. Conservatives urge the monarch to veto legislation, to stop a treacherous parliament defying “the will of the people”. Violence is in the air, most ominously in Northern Ireland. Welcome to the United Kingdom in the summer of 1914.

The crisis of 1914 far eclipsed Brexit, and brought Britain closer to revolution than at any time since the 17th century. The Times called it “one of the greatest crises in the history of the British race”, while Conservative election literature warned that Britain might soon be “stained with the blood of civil war”. Yet it offers some striking similarities with the present, and a warning of what could lie ahead.

The trigger was the election of December 1910. For the only time in British history, the result was a dead heat: the governing Liberal Party and its Conservative and Unionist opponents both won 272 seats. The Unionists won more votes, and a series of by-elections quickly made them the largest single grouping; but the outcome was a minority Liberal government, dependent chiefly on the Irish Nationalists. The price of Irish support was Home Rule, giving Ireland its own parliament with control over domestic legislation.

Home Rule was the Brexit controversy of its day. It had shattered the Liberal Party in the 1880s, rewired the party system and created new political identities that transcended party affiliation. For its supporters, it was an act of justice to Ireland and a restoration of its democratic rights. For its opponents, it was a menace to the empire, a blow to the Union and a betrayal of the Protestant population of Ulster, for whom Home Rule meant “Rome Rule”. For years, it had faced an insuperable barrier in the Upper House; but in 1911, the Parliament Act stripped the House of Lords of its veto. A Home Rule bill introduced in 1912 would now become law in 1914, whether the peerage approved or not.

That sparked an immediate crisis in Ulster. Half a million people signed the Ulster Covenant – a pledge to resist Home Rule by all possible means. This was backed up by a paramilitary army, ready to fight against a Home Rule Parliament. By 1914, the Ulster Volunteers had recruited more than 100,000 men, staffed by former British officers and armed by their supporters on the mainland.

They were backed to the hilt by the Conservative Party. The entire front bench signed a British version of the Covenant, making the Conservatives the only national party in the 20th century to sponsor a paramilitary army. Andrew Bonar Law, the pugnacious Conservative leader, told ministers that if they tried to suppress the Volunteers, “we should regard it as civil war”. A future Lord Chancellor, FE Smith, talked gleefully of ministers “swinging from the lamp posts of London”. In some of the most extraordinary images of the century, the leader of His Majesty’s Loyal Opposition was photographed inspecting the Ulster Volunteers, an illegal army pledged to bring down an Act of Parliament.

Crucially, the Conservatives did not simply argue that Home Rule was wrong. They rejected the democratic legitimacy of parliament, which they accused of defying the will of the people. Party literature told voters that “the House of Commons does not truly represent the people, nor do its votes represent the opinions of the electorate”. Conservatives talked openly of “breaking the parliamentary machine”, pitting “the Supremacy of the People” against the “paid puppets” of the House of Commons. Parliament was urged to surrender its functions to a referendum, to ensure that MPs could not “cut ‘the people’ out of the constitution”.

Even in an age before universal suffrage, the implications of this were incendiary. If parliament did not speak for the people, its laws were “tainted laws, of which Unionists did not admit the moral authority”. The Conservatives denounced the “coalition of minorities” that had locked their party out of power, insisting that it was not a legitimate government at all but “a self-appointed clique of politicians calling themselves ‘the cabinet’”. As such, Bonar Law declared, it had “lost the right to that obedience which can be claimed by a constitutional government”. At the Conservative Party conference in 1912, a speaker was shouted down for using the words: “We have a government.” He tried again: “A government so called”, prompting cheers and choruses of “Rule Britannia”.

By 1914, the atmosphere was volcanic. Conservative posters insisted that “every vote for the Liberals is a vote for civil war”. Campaign literature warned that “no method remains, except armed revolt, by which the country could make its will prevail”. Bonar Law told a demonstration at Blenheim that “there are things stronger than parliamentary majorities”, and he was almost certainly complicit in the gun-running at Larne in April, which supplied 35,000 rifles and three million cartridges to the Volunteers. The Primrose League, a Unionist support group, began fundraising for refugee camps, while MPs could be seen drilling their constituents in the parks.

With talk of revolution in the air, the outbreak of war in Europe was almost a welcome distraction. As the prime minister Herbert Asquith correctly foresaw, the European crisis would “take attention away from Ulster”. This, he wrote laconically, “is a good thing”.

What lessons might this teach for Brexit? Whatever one thinks of Boris Johnson, no one suspects him of supplying weapons to the Brexit Party or of stirring up mutiny in the armed forces. Yet some of the rhetoric of the Brexit debate has been scarcely less extreme. The tabloid press has waged a three-year war on a “Remainer parliament”, denouncing it as “a Westminster cabal” bent on frustrating the referendum result. The suspension of parliament was its natural outcome. Should the Remain parties succeed in displacing Boris Johnson, we will doubtless hear more of a “coalition of minorities”, engaged in a “conspiracy against the public”.

Yet Remainers should also be cautious. The prorogation of parliament is an abuse of power, but it is not a coup d’état. Talk of coups implies that the government is no longer legitimate, making its overthrow by unconstitutional and even violent means a patriotic and democratic duty. That, too, is not a claim to be made lightly.

Britain is approaching a situation in which Leavers deny the democratic legitimacy of parliament, while Remainers deny the democratic legitimacy of the government. As the ghosts of 1914 remind us, such rhetoric can lead to dark and dangerous places.

“The battle for parliament”: read the rest of our symposium on Britain’s political crisis here.