F or some years now, mainstream British politics has revolved increasingly obsessively around the question of how to stop Nigel Farage. What started a decade ago with Brexit may yet end in a general election that boils down to one question: do you or don’t you want to risk putting this man in Downing Street? That said, we still know surprisingly little about what a Reform government might mean in practice. Of course, it might never happen. But if it did, what exactly would Farage do with a majority that enabled him to fulfil his wildest dreams? And how well would an unwritten British constitution, still heavily reliant on good chaps voluntarily being good chaps, cope with full-fat populism? This is terrifically rich territory for a book, but what makes Times reporter Peter Chappell’s take so readable is its boldness.…