As coincidences go, this one should count as being extremely telling. On the morning of April 30, Britain's prime minister, Theresa May, appointed the 48-year-old Sajid Javid as home secretary, replacing her close ally, Amber Rudd, who was compelled to resign following a muddle over the country's immigration policy. Javid's appointment came after a handful of aficionados commemorated (not celebrated) 50 years of the (in)famous "Rivers of Blood" speech against 'coloured' immigration by Enoch Powell, a front-ranking Conservative politician.

In his speech to a Conservative conference on a sleepy Sunday on April 20, 1968, Powell — a Classics scholar whose early ambition was to be a viceroy of India — broke an unwritten rule of post-war British politics: he addressed the race question. Looking forward to the beginning of the 21st century, Powell prophesied: "Whole areas, towns and parts of towns across England will be occupied by sections of the immigrant and immigrant-descended population" whose presence would trigger race conflict — he possibly had in mind the race riots being witnessed that year in the United States of America. "We must be mad, literally mad, as a nation to be permitting the annual inflow of some 50,000 dependants, who are for the most part the material of the future growth of the immigrant-descended population. It is like watching a nation busily engaged in heaping up its own funeral pyre." Quoting Virgil — an allusion, he was to subsequently regret, was probably lost on both the audience and the media — he foresaw "the River Tiber foaming with much blood".

Powell's imagery was evocative, if inflammatory, and he was promptly disowned by the Conservative Party and spent the rest of his public life on the fringes — a man admired for his intellect and permanently despised for that one speech.

In the week that has witnessed the elevation of the son of an immigrant from Pakistan who arrived with just one pound in his pocket to the lofty post of home secretary, it is worth reflecting on Powell's speech. Was he the unsung prophet? Or, was he the arrogant pundit who just went horribly wrong and then adamantly stuck to his error?

Powell's motivation for delivering that carefully scripted speech is worth considering. "The supreme function of statesmanship," he noted, "is to provide against preventable evils." To him, it was unacceptable to believe that a problem or, indeed, an "evil" would disappear just because the British Establishment chose to pretend it didn't exist or because talking about it was socially unacceptable. He referred to a conversation with his constituents that in the coming days the country would not be worth living in for the next generation because the "black man will have the whip hand over the white one".

Powell, according to his biographer, Simon Heffer, "knew what would come". "I can already hear the chorus of execration. How dare I say such a horrible thing? How dare I stir up trouble and inflame feelings by repeating such a conversation? The answer is that I do not have the right not to do so. Here is a decent, ordinary Englishman, who in broad daylight in my own town says to me, his MP, that the country will not be worth living in for his children. I simply do not have the right to shrug my shoulders and think about something else. What he is saying, thousands and hundreds of thousands are saying and thinking... in the areas that are already undergoing the total transformation to which there is no parallel in a thousand years of English history."

For Powell, therefore, articulating an uncensored view of popular sentiment constituted the very essence of British democratic tradition. Here he was seemingly at variance with another great parliamentarian, Edmund Burke, who believed that "Parliament is a deliberative assembly of one nation, with one interest, that of the whole; where, not local purposes, not local prejudices ought to guide, but the general good, resulting from the general reason of the whole." In Burke's view, an MP once chosen, no longer represents the constituency, but Parliament as a whole.

Was Powell guilty of crossing all bounds by articulating the local disquiet in Wolverhampton? There is nothing to suggest this was so. By 1968, there was a recognition, cutting across all political parties, that the right of all Commonwealth citizens to unrestricted right of abode in the United Kingdom was simply untenable. The fact that cultural differences separated the immigrants from India, Pakistan, the Caribbean and Africa from the host community was undeniably a factor, as was the fear that the coming days would witness the creation of ethnic ghettos. The stringent immigration controls Powell argued for was to become a feature of British policy post-1968 until the 1980s when the expansion of the European Union set in motion a new wave of immigration from Eastern Europe.

Powell was not a racist steeped in cultural prejudice. He deeply admired India and, in his younger days, deified the British Empire. Once he even described the relationship between Britain and India as a "shared infatuation". However, after the post-war dissolution of Empire, Powell turned his back on the romantic concept of the Mother Country that would automatically play host to all its far-flung children. In a speech delivered in 1961, when he was still in the mainstream of politics and a rising star in the Conservative Party, he recalled that throughout the Empire phase, "the mother country remained unaltered... almost unconscious of the strange fantastic structure built around her — in modern parlance 'uninvolved'". He took this a step further by repudiating the fiction of the Commonwealth. "We have," he wrote in a Times article in 1986, "wronged... ourselves by constructing the pretence of a political entity, the Commonwealth, and acting as if it really existed."

Powell was quite ruthless in his logic. Once he concluded that the Empire was distant history and the Commonwealth idea illusory, he contested the very idea that Britain had an obligation to erstwhile British subjects. Consequently, he remained steadfast in his belief that, as he once told me over tea in 1986, that uprooting people was "unfair to both the Pathan and the Brummie".

Yet, Powell was only partly right in his belief that non-white immigrants into Britain would always remain a separate enclave. The spate of recruits fighting for the Islamic State in Syria and Iraq, and the curious un-British political culture in parts of East London and Birmingham may well reinforce the fears that were in evidence in 1968, as do the depredations of British Muslim 'grooming gangs' targeting vulnerable white girls in the north of England. However, against this are the many thousands of Asian professionals and entrepreneurs that have contributed so much to the British economy, not to mention the Black Britons that have added to the UK's reputation as a sports power, particularly in football and athletics.

Then there is the new home secretary who has promised to mould the country's immigration policies to correspond with 'British' values of fairness and justice. Growing up in a disadvantaged area, Javid was advised by his career counsellor in school to explore a future in repairing TV sets. That he broke an unfortunate stereotype, went to university, chalked out a global career in finance, got himself elected to Parliament and was finally elevated to the post of home secretary is revealing. It suggests that by the time the centenary of Powell's 1968 speech is commemorated, the immigrant threat will be as real as the likelihood of a Jacobite uprising. On his part, Powell may enjoy a footnote as a brilliant man who lost his way by picking on a wrong issue.