Forty years ago on April 20, 1968, Enoch Powell, a senior Tory member of the British House of Commons, spoke to a gathering of Conservatives in Birmingham , England , on immigration and citizenship in post-war Britain .

Powell warned against unrestricted immigration on the basis of numbers.

He indicated that “the significance and consequences of an alien element introduced into a country or population are profoundly different according to whether that element is 1% or 10%.”

Powell’s concerns about immigration into Britain from her former colonies got lost in the controversy that followed his speech.

He was roundly condemned for his inflammatory rhetoric when he declaimed: “As I look ahead, I am filled with foreboding. Like the Roman, I seem to see the River Tiber foaming with much blood.”

Powell was expelled from the shadow cabinet by Tory leader Edward Heath and his political career never recovered the promise of his early years, even though he sat in Parliament until 1987. Powell died in February 1998.

But with the London bombings of July 7, 2005, by “homegrown terrorists” of Pakistani origin, Powell’s warnings from four decades ago seem prophetic.

During the past 40 years British society and others in the West have changed greatly due to immigrants arriving from Asia, Africa, the Caribbean and Latin America .

In Canada , for instance, the numbers of foreign-born residents in Toronto – including some suburban areas such as Markham – are now more than half of the population.

As the profiles of western societies are altered by immigration, the concern or fear expressed by Powell has become more real in the post-Sept. 11, 2001 world of Islamist terrorism.

Immigration in general is a touchy subject given the West’s history of overseas colonies and empires, and any discussion of the linkage between immigration and terrorism is surely of an explosive nature that politicians will avoid.

The politics of multiculturalism is also unhelpful by penalizing those politicians – Powell being the most notable – willing to probe the negative effects of immigration.

But the link between immigration and terrorism needs examining and public discussion, not denial. Immigration policy that gets to be viewed as undermining security will lose public support.

Since 9/11, however, discussion of immigration policy merely in terms of the demographic needs of the West – with an aging population and a shriveled birthrate – without addressing concerns of public security is increasingly untenable.

Migration of people from their native homes to foreign lands is an old phenomenon. Its contributions have been mostly positive in the making of our hugely vibrant world.

There is nevertheless a negative side to migration when movements of people have adversely affected politics, worsened conflicts, inflamed bigotry, magnified fears of aliens and increased cultural tensions among ethnic communities.

In modern times, or at least during the past 50 years, migration has been mostly in one direction from non-western societies to the West.

What this mean for the West and its cultural inheritance, as the mix of its population changes in ways not fully anticipated, awaits broad and open public discussion.

This needs to happen, and it is best done in the relative political calm of the present, instead of under duress in a panic-stricken situation following another 9/11-type, or worse, terrorist outrage.