Britain’s new prime minister paused on the step of Downing Street, hesitating as that black door swung open. She’d just delivered her planned remarks, the ones about uniting the nation after years of division, about bringing the British family back together again and facing the future together.

She should be stepping over the threshold and into the job she never believed she’d hold. But instead, she turned back to the cameras for a few more, unscripted words. Her team would go nuts, but what the hell? She would not have the job for very long, so why not enjoy it?

“One other thing,” she added with a grin. “I wanted to say thank you. Thank you to the men who made this possible, the men who gave this great country its third female prime minister. Thank you, Boris Johnson and thank you, Jeremy Corbyn.”

And with a cheery wave, Prime Minister Jo Swinson turned and strolled into No 10 to greet her new staff.

How the Lib Dems could seize power By James Kirkup

Future historians of the Swinson premiership would spend much more time debating its beginning than its middle and its end; her time in office was, as she knew it would be, almost as short as that of her predecessor, Johnson.

Most of those historians agreed that it was Johnson who made the first move in the chain of events that put a Liberal Democrat in Downing Street and began the realignment of the British political system.

The first few months of the Johnson premiership went pretty much according to plan. The concessions on Brexit he sought from the EU27 were largely refused. That allowed him to confront Parliament: will you affirm or resist my choice to leave the EU on October 31 without a deal? Faced with resistance from most Labour MPs, a number of his own Tories and the prospect of outright obstruction in the Lords, he activated his plan for a general election.

This is where things started to go wrong for him and for Corbyn, and surprisingly right for Swinson, elected Lib Dem leader almost unnoticed in the same week Johnson became PM.

The Tory campaign immediately faced two huge and linked questions: what manifesto commitment would the party make on Brexit, and how would it deal with Nigel Farage and the Brexit Party? Johnson, convinced by his advisers that his first priority was to re-unite Right-wing Leave-voters under the Tory umbrella, opted to buy off Farage. All Tory candidates were required to sign a public pledge that they would vote to end British membership of the EU on Halloween, regardless of the circumstances.

It was enough for Farage to stand down his candidates; there was even a rumour, never convincingly denied, that he would take a peerage and a seat in Cabinet after the expected Tory rout of Corbyn’s divided, demoralised Labour Party.

How the Lib Dems could seize power By Peter Franklin

But that rout never materialised. For the second time in little more than two years, a Tory campaign directed by Lynton Crosby and focused on Brexit failed to secure outright victory. The campaign started with Tory defections, not to another party but to a new Independent Conservative Party whose members – including several recent ministers – were defending affluent Remain-voting seats across the south of England. The short timetable for the election left CCHQ unable to field “official” Conservative candidates against some of the new ICP candidates.

In some cases, that was enough for ICP members to scrape home. In others, places dominated by affluent graduates – places like Richmond upon Thames, St Albans, Oxford, Cambridgeshire, Mole Valley, Wandsworth, Cheltenham, Woking, Guildford, Waverley, Winchester and Bath – the Lib Dems captured (or recaptured) seats where Remain-minded voters rejected what Swinson repeatedly described as the “Johnson-Farage Brexit Party”, her leaflets and social media feeds heavy with photoshopped images of Johnson and Farage guffawing together.

The Lib Dems also strenuously denied involvement in the first DeepFake political ad in British history, an instantly-viral video of Johnson making a string of racist and sexist remarks while spilling red wine on a sofa. Elsewhere, in places like London, the Lib Dems directed their fire squarely at Corbyn. They were forced once again to deny involvement in another DeepFake video, this one depicting Corbyn addressing a small town hall meeting and speaking of his determination to free Britain of a European Union “that is run for the benefit of big business and Zionist bankers”.

“Honestly, I have no idea where these things come from,” said Swinson. “The Liberal Democrats are committed to the same old-fashioned, honest local campaigning that we’ve always done.”

Repeated demands from Labour and Tory alike that Facebook expunge the fake content were regretfully declined by Nick Clegg, the company’s Vice President of Global Affairs and Communications, who insisted that it would not interfere in the British democratic debate.

How the Lib Dems could seize power By Carl Miller

Labour avoided the sort of formal schism that the Tories experienced, but only because Corbyn did not even attempt to impose a single Brexit policy on his party, allowing Labour candidates to adopt positions ranging from No Brexit in Bristol to No Deal in Stoke-on-Trent.

The results of the election were described by one leading constitutional expert in an emotional late-night TV appearance as “a massive clusterfuck.” Labour technically “won” with 240 seats, marginally ahead of the rump Conservatives on 235. A total of 25 Independent Conservatives returned to the Commons, and the SNP hoovered up 50 Scottish seats.

Swinson marginally avoided losing her own seat, but hung on to cheer as 76 other Lib Dems were elected, taking seats from both Labour and the Tories.

The events that followed led to October 2019 being widely remembered as the most momentous month in British peacetime history. It started with Buckingham Palace signalling that the Queen would not immediately summon Corbyn and ask him to form a Government. As Corbyn’s few remaining media allies fulminated about a constitutional coup, it became clear why the Monarch had hesitated: Tom Watson, still Labour’s deputy leader, announced that he was resigning the Labour whip and would sit as a Social Democrat; he was quickly joined by more than 100 of his former Labour colleagues.

While Johnson, still technically Prime Minister, remained in No 10 facing Tory calls to quit in favour of Farage, Swinson made her move.

How the Lib Dems could seize power By James Kirkup

Inspired, as she later confirmed, by an old episode of The West Wing, she summoned TV cameras to film her walking slowly from the House of Commons up Whitehall then along the Mall to Buckingham Palace. Accompanied initially just by her Lib Dem colleagues, she was joined on the way first by Independent Conservative leader Rory Stewart, then by Watson, Emily Thornberry and Sir Keir Starmer.

By the time she reached the gates of the palace, she was able to deliver an impromptu speech declaring she and she alone could command a majority in the House of Commons and that she would wait outside until the Monarch asked her in.

For 57 minutes – later recalled as the longest hour in British history – Swinson waited, insisting that the light London rain was “nothing compared to Dumbarton”. Then the gates swung open.

In the hours that followed, the Queen faced immediate criticism for asking Swinson to form a government, because she did not obviously have the numbers to win a confidence vote: even with the SNP’s 50 votes, bought for the price of another Scottish independence referendum, the Swinson Coalition of Lib Dems, Independent Conservatives and Social Democrats would still be well short.

Then it emerged that the putative government would have a single purpose: the passage of a single piece of legislation.

The Democracy Day Bill, introduced on Trafalgar Day 2019, would have a number of consequences: Britain’s Article 50 notice to leave the European Union was withdrawn; the 2016 referendum to Leave or Remain would be run again in the spring of 2020. Prime Minister Swinson committed to campaign to remain, but also to resign the day after that referendum whatever the result. Britain would then hold a general election, its fourth in five years, to choose a government that would be elected having set out in its manifesto how it would honour the result of that referendum.

It took a couple of days of rather undignified taunting (“What are you afraid of, boys?”) but Swinson cajoled enough Conservative Leavers to signal support for her plan, declaring: “Let’s settle this once and for all.”

Barely noticed amid the tumult of debate around the new, temporary government and its single purpose were the clauses in the Democracy Day Bill. It made the holding of that second EU referendum conditional on the ending of the First Past the Post electoral system and the introduction of the d’Hondt method of voting for all future elections.