Yet his lurid warning about the dangers of mass immigration resonated with many Britons. He received tens of thousands of letters of support for what became known as the “rivers of blood” speech. Three days later, as a Labour government bill against racial discrimination was debated in Parliament, 1,000 dock workers marched from London’s East End to protest the “victimization” of Mr. Powell.

There are parallels between the way Mr. Powell gave voice to white working-class anxiety and Mr. Trump’s primary campaigning. And like Mr. Trump, Mr. Powell discovered a ready audience: A Gallup poll a few weeks later found that 74 percent of those surveyed agreed with what Mr. Powell had said. For immigrants like my father, who arrived in Britain from Pakistan in the early 1960s, it wasn’t Mr. Powell’s words that were frightening so much as that so many seemed to agree with them.

My father settled in Luton, an industrial town about 30 miles north of London that had a significant immigrant population. He worked on the assembly line at the Vauxhall car factory, the largest employer in the area. By the time my mother and siblings joined my father, in 1974, Mr. Powell was already a marginal figure in national politics. But his race-based views had been taken up by far-right groups like the National Front.

The National Front’s thuggish supporters were a visible, violent presence on the streets during my childhood. Mr. Powell’s speech also lent its anti-immigrant message a veneer of mainstream acceptability. The party’s program was crude — a ban on nonwhite immigration and repatriation for nonwhites — but, for a time, worryingly effective: In the 1979 general election, the National Front had more than 300 parliamentary candidates and won nearly 200,000 votes.

Growing up in the shadow of the “N.F.” and knowing that there were hundreds of thousands of Britons who wished to deport people like me induced both a profound anxiety and a deep conviction that I would never be fully accepted as British.

In recent years, the target of nativist anxiety about otherness in Britain has shifted from black to Muslim. From my background in Luton, I always looked to the United States as a place where almost everyone was “other,” from somewhere else; I imagined it as a nation that offered a welcome to all, regardless of color or creed.

That faith has been sorely tested by Mr. Trump. Like Mr. Powell, he demonstrates the appeal of a charismatic leader who presents himself as a principled truth-teller, the only man brave enough to break with the establishment consensus on immigration. As Mr. Powell did, Mr. Trump connects with voters — especially among the economically insecure white working class — who feel they’re being lied to by the political elite.