The rise of Nigel Farage has prompted political leaders across Ireland, Northern Ireland, Scotland and Wales to game the unthinkable: the breakup of the United Kingdom. Unionists who wish to save the union and nationalists who wish to end it are bracing for constitutional turmoil if Reform UK emerges triumphant – with Farage as prime minister or official leader of the opposition – after the next election. Representatives from each side believe a Farage-led government could trigger a hasty referendum on Irish unification and usher in Trump-style anti-immigration crackdowns that alienate the Celtic nations. The possibility of a strong Reform...