Enoch Powell was the quintessential clever fool. As a classical scholar and a fellow of Trinity College, Cambridge, he displayed dazzling intellectual gifts; in 1938, at the age of twenty-five, he became the youngest professor in the British Empire. A published poet, a talented clarinettist, a master of many languages, a translator of Herodotus and a devotee of Nietzsche, he enlisted as a private soldier at the outbreak of the Second World War and by 1945 had risen to the rank of brigadier. Powell voted Labour in the general election of that year and then joined the Conservative Research Department, where he distinguished himself through his incomparable zeal and industry. After being rejected by nineteen constituencies, he found a seat in Wolverhampton South West, which he won for the Tories in 1950. Despite his metallic voice, his robotic manner and his dour asceticism (tempered only by a passion for hunting), Powell’s abilities seemed to mark him out for high office.

For all his brilliance, though, he was palpably unsound. He rode his hobbyhorses almost to death and then, all too often, changed them midstream. He was an ideologue hopelessly in thrall to his own ideas, maintaining, for example, that Christ had not been crucified but stoned. In 1942, as the United States was getting the upper hand in the Pacific, he suggested that it was in Britain’s interest to preserve the balance of global power by challenging American naval dominance through means ‘not short even of alliance with Japan’. Having acquired a rare knowledge of India’s culture and architecture during the war, he lamented that his ambition to become viceroy had been shattered by its loss in 1947 and proposed reconquering the subcontinent with ten divisions, which prompted Churchill to ask if Powell was ‘all right’. Macmillan doubted it, making Powell health secretary in 1960 but moving his seat at the cabinet table because he could not ‘stand those mad eyes staring at me a moment longer’. Iain Macleod, a former friend, also came to regard him as a wild-eyed fanatic: ‘Poor Enoch, driven mad by the remorselessness of his own logic.’

The task of tracing the course of Powell’s ideas in all their contortions and contradictions, and assessing their impact, is not easy. But Paul Corthorn accomplishes it admirably. His book is clear, coherent and concise. It is based on a vast amount of reading and research. All told, it is a model of scholarship – save in one respect. Seeking the goal of academic objectivity, Corthorn adopts as far as possible ‘a detached, impartial perspective’. Thus he refuses to discuss whether Powell was right or wrong about the two major causes which he championed and which today have coalesced in Brexit, namely opposition to immigration and to the European Community. Yet the role of the historian is not just to elicit and present evidence but to weigh it too. To chronicle the past is all very well, but historical writing also requires interpretation and the exercise of judgement, including value judgement.

Corthorn does at least argue that what united Powell’s maverick notions was anguish about Britain’s post-imperial decline. So it was that Powell waxed hysterical about the prospect of the country’s native stock being diluted by alien blood, asserting that ‘the English are a white nation’ and warning that the arrival of 55,000 Ugandan Asians would be a ‘national catastrophe’. And he declared that belonging to the European Community abrogated the supremacy of Parliament and destroyed ‘all prospect of national rebirth’. On the other hand, as Corthorn demonstrates, he was consistently inconsistent. His dissident impulses were legion. Like Gladstone, Powell could convince others of some things and convince himself of anything. In this respect he also resembled Churchill, who was said by Lord Beaverbrook to have held every opinion on every subject.

In 1950 Powell was still advocating greater imperial unity, imperial preference and the free movement of people within the British Empire; but he soon began to disparage the Empire and dismissed the Commonwealth as a sham. He opposed Britain’s acquisition of nuclear weapons but accepted their retention to avert blackmail by countries that did have them. He vacillated in his attitude towards NATO and was so hostile to the United States that he hankered for alignment with the Soviet Union and ‘the death and burial of the American Empire’. Powell condemned state planning and asserted (repeating Churchill’s calamitous claim of 1945) that Attlee’s government would require some kind of Gestapo to enforce its regulations. Yet he acknowledged that state intervention was necessary to avert social evils and at the ministry of health he made long-term plans for the NHS. This he supported through thick and thin, despite his extreme free-market beliefs. Indeed, he expanded it, recruiting eighteen thousand doctors from India and Pakistan, who provided ‘a useful and substantial reinforcement of the staffing of our hospitals’.

However, Powell was increasingly concerned about ‘massive coloured immigration’. He called for ‘voluntary repatriation’ (how voluntary was unclear) and opposed Roy Jenkins’s Race Relations Bill, arguing that tensions between different communities were the result not of ‘discrimination by white against coloured but of insolence by coloured towards white’. Then in 1968 Powell delivered his ‘Rivers of Blood’ speech, which was less an oration than an apocalyptic vision, one that transformed him from politician into prophet. Seeing the level of immigration from outside Europe, he said, was like watching the nation ‘heaping up its own funeral pyre’. Soon, he suggested, ‘the black man will have the whip hand over the white man’. Powell’s locus classicus involved an unidentified little old white lady surrounded by aliens, who had excrement pushed through her letter box and was followed in the street by ‘wide-grinning piccaninnies’. Such provocative language, echoed today, of course, by Boris Johnson, exacerbated racial tensions and legitimised xenophobia.

Johnson is also indebted to Powell for his ‘do or die’ rhetoric about leaving the EU, though perhaps he forgets that this phrase comes from ‘The Charge of the Light Brigade’, Tennyson’s celebration of that other national triumph. Powell, who had earlier supported membership on economic grounds, decried it after 1969 as a mortal threat to British sovereignty. Europe, he proclaimed, was ‘an issue literally of life and death’. Thus he endorsed the Labour Party in 1974 and 1979, when it was at its most Eurosceptic, only to throw his weight behind Margaret Thatcher in 1988 when (in Bruges) she denounced the emergence of a ‘European super-state’. Like others, Thatcher was somewhat mesmerised by Powell. And he laid much of the groundwork for the policies she pursued: monetarism, privatisation, deregulation, anti-unionism, low direct taxation. As she herself observed, Powell ‘commanded influence without power’.

Corthorn’s book preserves a studious neutrality about all this, where a more critical appraisal might have attributed many of Britain’s subsequent ills to the Powell effect. Deregulation in the 1980s stimulated casino capitalism, which in turn led to grotesque inequalities of wealth and the 2008 financial crash. Privatisation aggravated the housing shortage, produced extortionate private monopolies in such areas as water and energy supply and resulted in fiascos such as the recent crisis in the probation service. Powell undoubtedly helped to validate Theresa May’s ‘hostile environment’ for illegal immigrants, which precipitated the Windrush scandal. And, of course, he inspired the disaster of Brexit. It’s hard not to conclude that the gospel according to Enoch was damnable. He remains the best possible advertisement for unidea’d conservatism.