'Anyone who wishes to understand why Brexit is so intractable should read this book. I can think of several MPs who ought to.' The TimesFor the past two decades, you could cross the border between Northern Ireland and the Republic half a dozen times without noticing or, indeed, turning off the road you were travelling. It cuts through fields, winds back-and-forth across roads, and wends from Carlingford Lough to Lough Foyle. It is frictionless - a feat sealed by the Good Friday Agreement. Before..