ON APRIL 20th 1968 Enoch Powell rose to give a speech before an audience of Conservative Party activists in the Midland Hotel in Birmingham. Normally such an occasion, on a Saturday afternoon, would have attracted little attention. But the shadow defence secretary, dressed formally, as ever, in a three-piece suit, had other ideas. Powell had invited the TV cameras, and promised one journalist that his speech was “going to go up, ‘fizz’, like a rocket; but whereas all rockets fall to Earth, this one is going to stay up.” He was right.

This was Powell’s “rivers of blood” speech, so named after the peroration. It was a direct and provocative assault on immigration from the Commonwealth, quoting the fears of one constituent that “in 15 or 20 years’ time, the black man will have the whip hand over the white man.” It caused outrage at the time—Powell was sacked from the Tories’ front bench—and still does. Many objected even to an actor reading out his words in a recent BBC radio programme to mark the anniversary.

Powell’s main contention was that if mass immigration continued, there would be civil strife. “Like the Roman,” he warned, “I seem to see ‘the River Tiber foaming with much blood’.” The line was from Virgil but the apocalyptic tone was borrowed from America, ablaze with riots after the murder of Martin Luther King on April 4th that year. Powell, “filled with foreboding”, implied that Britain could not continue to absorb the current number of immigrants without mass violence.

The subsequent 50 years have disproved that idea. Today’s levels of immigration dwarf those at the time of Powell’s speech (see chart). About 14% of Britain’s population is foreign-born, nearly treble the proportion in 1968. Non-whites made up 14% of the population at the last census, in 2011; non-British whites (mainly Europeans) a further 5%. A tenth of adults reported that they were in mixed-race relationships. All this might have shocked Powell, who died in 1998. Yet the conflagration that he predicted has not materialised.

Birmingham itself provides as good a case study as any. Today half of all the non-white people in Britain live in the three largest cities of London, Birmingham and Manchester. Birmingham exemplifies the trend towards what academics call superdiversity. In the past, minority ethnic groups tended to cluster together. Now, unprecedented numbers of people of different ethnicities are mixing. No ward in Birmingham has fewer than 32 ethnic groups, says Jenny Phillimore of Birmingham University. At the extreme is Handsworth, whose 31,000 residents hail from 170 different countries. Here, says Ms Phillimore, “virtually everyone can fit in”.

This is reflected in the region’s politics. Powell’s nearby former constituency of Wolverhampton South West was until 2015 represented by Paul Uppal, a Sikh (and Conservative), and is now held by Eleanor Smith of the Labour Party, whose mother immigrated from Barbados in 1954 to work in the National Health Service. Ms Smith remembers her mother’s distress at Powell’s speech, which called for voluntary repatriation—something which was Conservative Party policy at the time. She had been encouraged to come to Britain at a time of labour shortages, and was now being told to go home.

Superdiversity in Birmingham and other cities is evidence of integration, but, cautions Eric Kaufman of Birkbeck College, University of London, it has in some cases meant less contact between whites and ethnic minorities. There has been some “white flight” from superdiverse areas, he says, as whites have moved out of the poorer areas where migrants gather, to the suburbs. The end result is that “minorities are mixing with each other, but less so with the white British.”

An official review into integration in 2016 by Dame Louise Casey found that white-British and Irish people were the least likely to have ethnically mixed social networks. It also highlighted the socio-economic exclusion and consequent isolation of some Pakistani and Bangladeshi communities. They have the lowest levels of English-language proficiency of any minority group; more than a fifth of Muslim women cannot speak the language well.

Such findings mean that Powell still has admirers. There was recently an application for him to be honoured with a blue plaque outside his home in Wolverhampton (thousands have petitioned against it). But the real effect of his “rivers of blood” speech was not to open a frank discussion on such matters, but to stifle it. As Dame Louise argues, by talking about immigration in such menacing tones, Powell shut down sensible debate about the subject for decades. One consequence is that some problems have not been tackled, leading to outcomes like the relative isolation of Pakistani women. “We have had our heads in the sand about this,” she laments.

Powell’s speech may also have had an unexpected impact on another of his obsessions: Britain’s relationship with the European Union. Migration had been a taboo subject for decades, because of its association with race. But after the number of mainly white immigrants from eastern Europe shot up in the early 2000s, pent-up worries about migration and integration were suddenly and explosively aired. The subsequent Brexit referendum of 2016 was lost largely on the issue of migration.

Half a century on from Powell’s speech, the blood still shows no sign of foaming. But the lasting and malign effect of his intervention on the way in which race and migration are discussed, or not discussed, holds a lesson for all politicians about the power of their words.