The supreme function of statesmanship is to provide against preventable evils. In seeking to do so, it encounters obstacles which are deeply rooted in human nature.

One is that by the very order of things such evils are not demonstrable until they have occurred: at each stage in their onset there is room for doubt and for dispute whether they be real or imaginary. By the same token, they attract little attention in comparison with current troubles, which are both indisputable and pressing: whence the besetting temptation of all politics to concern itself with the immediate present at the expense of the future.

Above all, people are disposed to mistake predicting troubles for causing troubles and even for desiring troubles: "If only," they love to think, "if only people wouldn't talk about it, it probably wouldn't happen."

Perhaps this habit goes back to the primitive belief that the word and the thing, the name and the object, are identical.

At all events, the discussion of future grave but, with effort now, avoidable evils is the most unpopular and at the same time the most necessary occupation for the politician. Those who knowingly shirk it deserve, and not infrequently receive, the curses of those who come after.

A week or two ago I fell into conversation with a constituent, a middle-aged, quite ordinary working man employed in one of our nationalised industries.

After a sentence or two about the weather, he suddenly said: "If I had the money to go, I wouldn't stay in this country." I made some deprecatory reply to the effect that even this government wouldn't last for ever; but he took no notice, and continued: "I have three children, all of them been through grammar school and two of them married now, with family. I shan't be satisfied till I have seen them all settled overseas. In this country in 15 or 20 years' time the black man will have the whip hand over the white man."

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 fellow Englishman, who in broad daylight in my own town says to me, his Member of Parliament, that his 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 - not throughout Great Britain, perhaps, but in the areas that are already undergoing the total transformation to which there is no parallel in a thousand years of English history.

In 15 or 20 years, on present trends, there will be in this country three and a half million Commonwealth immigrants and their descendants. That is not my figure. That is the official figure given to parliament by the spokesman of the Registrar General's Office.

There is no comparable official figure for the year 2000, but it must be in the region of five to seven million, approximately one-tenth of the whole population, and approaching that of Greater London. Of course, it will not be evenly distributed from Margate to Aberystwyth and from Penzance to Aberdeen. Whole areas, towns and parts of towns across England will be occupied by sections of the immigrant and immigrant-descended population.

As time goes on, the proportion of this total who are immigrant descendants, those born in England, who arrived here by exactly the same route as the rest of us, will rapidly increase. Already by 1985 the native-born would constitute the majority. It is this fact which creates the extreme urgency of action now, of just that kind of action which is hardest for politicians to take, action where the difficulties lie in the present but the evils to be prevented or minimised lie several parliaments ahead.

The natural and rational first question with a nation confronted by such a prospect is to ask: "How can its dimensions be reduced?" Granted it be not wholly preventable, can it be limited, bearing in mind that numbers are of the essence: the significance and consequences of an alien element introduced into a country or population are profoundly different according to whether that element is 1 per cent or 10 per cent.

The answers to the simple and rational question are equally simple and rational: by stopping, or virtually stopping, further inflow, and by promoting the maximum outflow. Both answers are part of the official policy of the Conservative Party.

It almost passes belief that at this moment 20 or 30 additional immigrant children are arriving from overseas in Wolverhampton alone every week - and that means 15 or 20 additional families a decade or two hence. Those whom the gods wish to destroy, they first make mad. 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. So insane are we that we actually permit unmarried persons to immigrate for the purpose of founding a family with spouses and fiancés whom they have never seen.

Let no one suppose that the flow of dependants will automatically tail off. On the contrary, even at the present admission rate of only 5,000 a year by voucher, there is sufficient for a further 25,000 dependants per annum ad infinitum, without taking into account the huge reservoir of existing relations in this country - and I am making no allowance at all for fraudulent entry. In these circumstances nothing will suffice but that the total inflow for settlement should be reduced at once to negligible proportions, and that the necessary legislative and administrative measures be taken without delay.

I stress the words "for settlement." This has nothing to do with the entry of Commonwealth citizens, any more than of aliens, into this country, for the purposes of study or of improving their qualifications, like (for instance) the Commonwealth doctors who, to the advantage of their own countries, have enabled our hospital service to be expanded faster than would otherwise have been possible. They are not, and never have been, immigrants.

I turn to re-emigration. If all immigration ended tomorrow, the rate of growth of the immigrant and immigrant-descended population would be substantially reduced, but the prospective size of this element in the population would still leave the basic character of the national danger unaffected. This can only be tackled while a considerable proportion of the total still comprises persons who entered this country during the last ten years or so.

Hence the urgency of implementing now the second element of the Conservative Party's policy: the encouragement of re-emigration.

Nobody can make an estimate of the numbers which, with generous assistance, would choose either to return to their countries of origin or to go to other countries anxious to receive the manpower and the skills they represent.

Nobody knows, because no such policy has yet been attempted. I can only say that, even at present, immigrants in my own constituency from time to time come to me, asking if I can find them assistance to return home. If such a policy were adopted and pursued with the determination which the gravity of the alternative justifies, the resultant outflow could appreciably alter the prospects.

The third element of the Conservative Party's policy is that all who are in this country as citizens should be equal before the law and that there shall be no discrimination or difference made between them by public authority. As Mr Heath has put it we will have no "first-class citizens" and "second-class citizens." This does not mean that the immigrant and his descendent should be elevated into a privileged or special class or that the citizen should be denied his right to discriminate in the management of his own affairs between one fellow-citizen and another or that he should be subjected to imposition as to his reasons and motive for behaving in one lawful manner rather than another.

There could be no grosser misconception of the realities than is entertained by those who vociferously demand legislation as they call it "against discrimination", whether they be leader-writers of the same kidney and sometimes on the same newspapers which year after year in the 1930s tried to blind this country to the rising peril which confronted it, or archbishops who live in palaces, faring delicately with the bedclothes pulled right up over their heads. They have got it exactly and diametrically wrong.

The discrimination and the deprivation, the sense of alarm and of resentment, lies not with the immigrant population but with those among whom they have come and are still coming.

This is why to enact legislation of the kind before parliament at this moment is to risk throwing a match on to gunpowder. The kindest thing that can be said about those who propose and support it is that they know not what they do.

Nothing is more misleading than comparison between the Commonwealth immigrant in Britain and the American Negro. The Negro population of the United States, which was already in existence before the United States became a nation, started literally as slaves and were later given the franchise and other rights of citizenship, to the exercise of which they have only gradually and still incompletely come. The Commonwealth immigrant came to Britain as a full citizen, to a country which knew no discrimination between one citizen and another, and he entered instantly into the possession of the rights of every citizen, from the vote to free treatment under the National Health Service.

Whatever drawbacks attended the immigrants arose not from the law or from public policy or from administration, but from those personal circumstances and accidents which cause, and always will cause, the fortunes and experience of one man to be different from another's.

But while, to the immigrant, entry to this country was admission to privileges and opportunities eagerly sought, the impact upon the existing population was very different. For reasons which they could not comprehend, and in pursuance of a decision by default, on which they were never consulted, they found themselves made strangers in their own country.

They found their wives unable to obtain hospital beds in childbirth, their children unable to obtain school places, their homes and neighbourhoods changed beyond recognition, their plans and prospects for the future defeated; at work they found that employers hesitated to apply to the immigrant worker the standards of discipline and competence required of the native-born worker; they began to hear, as time went by, more and more voices which told them that they were now the unwanted. They now learn that a one-way privilege is to be established by act of parliament; a law which cannot, and is not intended to, operate to protect them or redress their grievances is to be enacted to give the stranger, the disgruntled and the agent-provocateur the power to pillory them for their private actions.

In the hundreds upon hundreds of letters I received when I last spoke on this subject two or three months ago, there was one striking feature which was largely new and which I find ominous. All Members of Parliament are used to the typical anonymous correspondent; but what surprised and alarmed me was the high proportion of ordinary, decent, sensible people, writing a rational and often well-educated letter, who believed that they had to omit their address because it was dangerous to have committed themselves to paper to a Member of Parliament agreeing with the views I had expressed, and that they would risk penalties or reprisals if they were known to have done so. The sense of being a persecuted minority which is growing among ordinary English people in the areas of the country which are affected is something that those without direct experience can hardly imagine.

I am going to allow just one of those hundreds of people to speak for me:

“Eight years ago in a respectable street in Wolverhampton a house was sold to a Negro. Now only one white (a woman old-age pensioner) lives there. This is her story. She lost her husband and both her sons in the war. So she turned her seven-roomed house, her only asset, into a boarding house. She worked hard and did well, paid off her mortgage and began to put something by for her old age. Then the immigrants moved in. With growing fear, she saw one house after another taken over. The quiet street became a place of noise and confusion. Regretfully, her white tenants moved out.

“The day after the last one left, she was awakened at 7am by two Negroes who wanted to use her 'phone to contact their employer. When she refused, as she would have refused any stranger at such an hour, she was abused and feared she would have been attacked but for the chain on her door. Immigrant families have tried to rent rooms in her house, but she always refused. Her little store of money went, and after paying rates, she has less than £2 per week. “She went to apply for a rate reduction and was seen by a young girl, who on hearing she had a seven-roomed house, suggested she should let part of it. When she said the only people she could get were Negroes, the girl said, "Racial prejudice won't get you anywhere in this country." So she went home.

“The telephone is her lifeline. Her family pay the bill, and help her out as best they can. Immigrants have offered to buy her house - at a price which the prospective landlord would be able to recover from his tenants in weeks, or at most a few months. She is becoming afraid to go out. Windows are broken. She finds excreta pushed through her letter box. When she goes to the shops, she is followed by children, charming, wide-grinning piccaninnies. They cannot speak English, but one word they know. "Racialist," they chant. When the new Race Relations Bill is passed, this woman is convinced she will go to prison. And is she so wrong? I begin to wonder.”

The other dangerous delusion from which those who are wilfully or otherwise blind to realities suffer, is summed up in the word "integration." To be integrated into a population means to become for all practical purposes indistinguishable from its other members.

Now, at all times, where there are marked physical differences, especially of colour, integration is difficult though, over a period, not impossible. There are among the Commonwealth immigrants who have come to live here in the last fifteen years or so, many thousands whose wish and purpose is to be integrated and whose every thought and endeavour is bent in that direction.

But to imagine that such a thing enters the heads of a great and growing majority of immigrants and their descendants is a ludicrous misconception, and a dangerous one.

We are on the verge here of a change. Hitherto it has been force of circumstance and of background which has rendered the very idea of integration inaccessible to the greater part of the immigrant population - that they never conceived or intended such a thing, and that their numbers and physical concentration meant the pressures towards integration which normally bear upon any small minority did not operate.

Now we are seeing the growth of positive forces acting against integration, of vested interests in the preservation and sharpening of racial and religious differences, with a view to the exercise of actual domination, first over fellow-immigrants and then over the rest of the population. The cloud no bigger than a man's hand, that can so rapidly overcast the sky, has been visible recently in Wolverhampton and has shown signs of spreading quickly. The words I am about to use, verbatim as they appeared in the local press on 17 February, are not mine, but those of a Labour Member of Parliament who is a minister in the present government:

'The Sikh communities' campaign to maintain customs inappropriate in Britain is much to be regretted. Working in Britain, particularly in the public services, they should be prepared to accept the terms and conditions of their employment. To claim special communal rights (or should one say rites?) leads to a dangerous fragmentation within society. This communalism is a canker; whether practised by one colour or another it is to be strongly condemned.'

All credit to John Stonehouse for having had the insight to perceive that, and the courage to say it.

For these dangerous and divisive elements the legislation proposed in the Race Relations Bill is the very pabulum they need to flourish. Here is the means of showing that the immigrant communities can organise to consolidate their members, to agitate and campaign against their fellow citizens, and to overawe and dominate the rest with the legal weapons which the ignorant and the ill-informed have provided. As I look ahead, I am filled with foreboding; like the Roman, I seem to see "the River Tiber foaming with much blood."

That tragic and intractable phenomenon which we watch with horror on the other side of the Atlantic but which there is interwoven with the history and existence of the States itself, is coming upon us here by our own volition and our own neglect. Indeed, it has all but come. In numerical terms, it will be of American proportions long before the end of the century.

Only resolute and urgent action will avert it even now. Whether there will be the public will to demand and obtain that action, I do not know. All I know is that to see, and not to speak, would be the great betrayal.