Leaving the European Union is not the only split British Prime Minister Boris Johnson has to worry about.
Johnson's election victory last week may let him fulfil his campaign promise to "get Brexit done", but could imperil the future of the United Kingdom of England, Scotland, Wales and Northern Ireland.
In his victory speech, Johnson said the election result proved leaving the EU was "the irrefutable, irresistible, unarguable decision of the British people".
Arguably, though, it isn't. It's the will of the English, who make up 56 million of the UK's 66 million people.
During Britain's 2016 referendum on EU membership, England and Wales voted to leave the bloc; Scotland and Ireland didn't.
In last week's election, England elected 345 Conservative lawmakers — all but 20 of the 365 House of Commons seats Johnson's party won across the UK.
In Scotland, 48 of the 59 seats were won by the Scottish National Party, which opposes Brexit and wants Scottish independence.
In 2014, when Scotland held a referendum on seceding from the UK, the "remain" side won 55 to 45 per cent. At the time, the referendum was billed as a once-in-a-generation decision. But the SNP argues Brexit has changed everything because Scotland now faces being dragged out of the EU against its will.
Post-election, SNP leader Nicola Sturgeon says Johnson "has no mandate whatsoever to take Scotland out of the EU" and Scotland must be able to decide its future in a new independence referendum. Johnson insists he will not approve one.
The Scotsman newspaper summed up the showdown with front-page face-to-face images of Sturgeon and Johnson: "Two landslides. One collision course."
"What we've got now is pretty close to a perfect storm," said historian Tom Devine, professor emeritus at the University of Edinburgh. He said the UK was facing an "unprecedented constitutional crisis" as Johnson's refusal to approve a referendum fuelled growing momentum for Scottish independence.
Politically and legally, it's a stalemate. Without the approval of the UK Government, a referendum would not be legally binding. London could simply ignore the result, as the Spanish government did when Catalonia held an unauthorised independence vote in 2017.
Then there is Northern Ireland. For the first time, it elected more lawmakers who favour union with Ireland than remaining in the UK.
The Irish border issue has proved the most difficult in Brexit negotiations.
"Once you put a border between Northern Ireland and the rest of the United Kingdom, Northern Ireland's going to be part of a united Ireland for economic purposes," Jonathan Powell, who helped negotiate Northern Ireland's 1998 peace accord, told the BBC. "That will increase the tendency toward a united Ireland for political reasons, too.
"I think there is a good chance there will be a united Ireland within 10 years."
In Scotland, Devine also thinks the days of the Union may be numbered.
"I think it's more likely than not that the UK will come to an end over the next 20 to 30 years."
Overhaul of Whitehall planned
Boris Johnson is plotting a dramatic overhaul of Whitehall after his landslide election victory, in a drive to demonstrate that the Government "works for the people".
Dominic Cummings, Johnson's chief aide, is to spearhead plans for radical reforms to the civil service, including a review of the processes for hiring and firing officials, to ensure Whitehall delivers the Prime Minister's agenda. He has previously complained "almost no one is ever fired" in Whitehall, during a lecture in which he set out a "to-do list" he had maintained in case "I ever manage to get control of No 10."
It suggests Johnson's programme for the next five years is likely to be far more radical than the agenda he set out after taking over from Theresa May in July.
Cummings worked as a special adviser to Michael Gove during the coalition years. He led the official Vote Leave campaign in 2016, and is a long-standing critic of Whitehall.
- AP, additional reporting Telegraph Media Group