When writing his magnificent life of Robert Peel, Douglas Hurd found himself caught up again in a debate that has always fascinated him as a former diplomat and Foreign Secretary - the argument between the noisy popular liberal interventionist approach and the more conservative diplomatic approach concentrating on co-operation between other nations. The argument has run for two centuries - and is at the heart of heated discussion on both sides of the Atlantic today. Hurd concentrates on personalities and circumstances. He begins with the dramatic antagonism after Waterloo between Canning (liberal, populist, interventionist) and Castlereagh (institutions, compromise, real politics) - the last occasion on which ministerial colleagues fought a duel. A generation later comes Palmerston vs Aberdeen, from which Palmerston, the noisy interventionist, emerged the victor. A fascinating, but forgotten vignette is provided by the quarrel between Disraeli and his old friend and Foreign Secretary, Lord Derby, which led to Derby resigning as a protest against jingoism and Disraeli spreading the rumour that Lady Derby was leaking secrets to the Russian Ambassador. Salisbury and then Edward Grey wrestled with the same dilemma in the context of imperialism (Salisbury) and the European balance of power (Grey). Between the wars, another vignette describing Austen Chamberlain, the decent, monocled Foreign Secretary who began as an idealist (Locarno Treaty) and ended as a passionate opponent of appeasement. Finally Eden and Bevin, from wholly different backgrounds, combined with the Americans to create a post-war compromise, which served its purpose for half a century, but is coming apart today as the old questions resurface in new and savage forms in an era of terrorism and racial conflict.