“IF ENOCH POWELL were alive today, what would he have to say about the current security situation?” It was a typical Any Questions debating point — the equivalent of rolling a grenade into a crowded pub, then standing back to see what would happen. Within minutes, the discussion on Radio 4 had become a full-scale argument about Islamic terrorism, multiculturalism, free trade and Polish plumbers. From this week, it is also about Romanians and Bulgarians, rampant Aids and the white slave traffic. The debate about immigration is as inflammatory today as it was when Powell articulated it in 1968. It is also as dangerously confused.

The answer Powell himself would undoubtedly have given is: “I told you so.” He would have claimed prescience about the numbers flooding into Britain from abroad, he would say that multiculturalism (which he referred to it in those days as “communalism”) had demonstrably failed, and he would have argued that the growth of immigrant communities had undermined the security of the State. He said as much in his infamous “rivers of blood” speech, when he spoke of “dangerous and divisive elements” within the immigrant community, who would use Britain’s well-intentioned race relations laws “to organise and consolidate their members, to agitate and campaign against their fellow-citizens, and to overawe and dominate the rest”.

It was a blatantly racist speech, playing to the most basic fears of the white population at the time about the growth of immigration from the Commonwealth. It was also wrong. Powell presumed that the majority of immigrants would become increasingly alienated from society and that, as their numbers increased, they would seek to assert their domination over the native British. He thought that the sheer weight of numbers would simply overwhelm white communities, who would become, to quote him, “strangers in their own country”. He predicted intolerable tensions as a result, with a system of “one-way privilege” operating in favour of immigrants. That has not happened. There have been flashpoints along the way — race riots in Brixton, Bristol and the North of England, racist attacks and murders, and the worrying alienation of Muslim minorities. But the breakdown that he predicted has not happened; Powell’s nightmare vision has not materialised.

It has not, however, gone away. In different forms, it is summoned up to warn us of the threat from Islamic extremists, from asylum-seekers, and now the influx of immigrants from Eastern Europe. The latest figures, published yesterday, show that more than 400,000 migrants from the former Soviet bloc had been registered for work here over the past two years, the majority from Poland. From next year, another influx from Romania and Bulgaria is predicted. Unlike other EU countries, Britain, with the Irish Republic, has maintained an “open doors” policy, with no restriction on entry. Ministers are beginning to retreat from that, indicating that from now on immigration will be “properly managed and controlled”.

They are doing so, however, not because of logic but because of fear — the same irrational fear that Powell so successfully played on. The red-top press has carried a ritual diet of horror stories about Romanian gangsters, the spread of Aids from immigrants, and the massage parlours that will rapidly blight our inner cities when the “floodgates” open. Crime will increase and the pressure on health and social services, will, it says, become intolerable. This argument in turn merges into mounting concerns about multiculturalism, most elegantly expressed by David Goodhart in Prospect magazine, and now almost part of the mainstream of intellectual debate. This claims that patriotism and the culture of Britishness has been undermined because ethnic communities have been allowed to develop their own identities, and that this in turn has led to the radicalising of Muslim youth; the latest adherent is George Alagiah, the BBC newsreader, who claims that diversity and fundamentalism have developed hand in hand.

Even Polly Toynbee, The Guardian’s liberal standard-bearer, has become part of the bandwagon, arguing for greater control of immigration, on the ground that cheap labour is preventing Britain’s unemployed from training to compete. The gap between rich and poor, she says, is widening thanks to the ready availability of immigrant workers.

As so often, there is a grain of truth in some of these arguments — but collectively, they amount to a lie. Immigration has, by and large, been of enormous benefit to Britain. It has helped to transform our economy, enrich our cultural life, support our public services and improve our image abroad. It would be inconceivable to imagine our health or transport systems functioning without it. It fills a skills gap among doctors and teachers. It allows the nation’s corner shops to survive. Toynbee’s argument about cheap labour could have been deployed at any time over the past 50 years, and would have prevented buses and trains from functioning, hospitals being cleaned, schools being staffed and maintained.

At the same time I am beginning to find the argument against multiculturalism tendentious — it plays too easily to the bias of racism, and it is manna for the British National Party; radicalised Muslims are not, by and large, immigrants — they are born and raised in Britain, their extremism owing more to events abroad than diversity in this country. As for the suggestion that Romanians and Bulgarians will do little more than import crime and sexual disease — it is the grossest of slurs.

I have no doubt that mass immigration needs to be controlled, but rather than new restrictions the current rules should be managed more effectively and with greater humanity. This is too important an issue to be hijacked by prejudice disguising itself as rational debate. Unless we distinguish carefully between its differing strands, we might just as well give in to racism and say that Enoch was right all along.

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