Britain is poised at two historic turning points — and they go together. Very much depends on the outcome.

Rapid population growth, driven by the highest immigration in our history, is destabilising and transforming its population, its environment and its ethnic make-up into something quite new.

At the same time, the UK faces a choice about leaving the EU or remaining in it.

Some welcome the growth of the population and the increased diversity that it brings. For those who do not, leaving the EU offers a possibility of moderating at least some of that growth, keeping the UK in something like its present size and shape.

However, that is only a possibility.

The G7 talks in Japan this week involving David Cameron no doubt had the prospect of Brexit at the forefront

By itself, Brexit might change nothing; for it would depend on the choices made by any post-Brexit government, in particular on also leaving the European Economic Area (which includes all EU member states plus Iceland, Liechtenstein and Norway) and ending the commitment to the free movement of labour.

Until 1997, immigration had been off the policy agenda for 20 years, thanks to an uneasy political consensus to limit inflows. Although trending slightly upwards, immigration was not then very controversial.

However, the Blair government began to take down the barriers to migration.

According to Blair aide Andrew Neather, one of the aims of the New Labour policy of opening up the UK to mass immigration was to ‘rub the Right’s nose in diversity’, promoting permanent ethnic change to the permanent electoral advantage of Labour.

The steps then taken provoked a rapid upsurge in net migration (inflow minus outflow), which continues to reach record levels: 3.3 million immigrants came to the UK from 2001 to 2014.

Immigration, mostly then from outside the EU, had already reached record levels when, in 2004, the Blair government, alone among the major economies of the West, allowed free entry for work to the new Eastern European EU accession countries.

Those countries had low levels of income and low social and political development relative to the EU average.

Everything pointed to a very large influx, but the government fatuously predicted that ‘13,000 per year’ would enter. Officially, 53,000 entered in the first year and 76,000 the next; these figures are now known to be substantial underestimates.

Vote Leave have used the population crisis as a key point in their pro-Brexit campaign

At any rate, by 2013, 1.24 million people born in Eastern Europe were living in the UK, compared with 170,000 in 2004 — the biggest inflow in British history.

No forward planning or provision whatsoever was made for the Blairite influx. Indeed, it has been so great that it would have been difficult to make adequate provision. Hence many of our present problems.

Naturally, many of these arise straightforwardly from the pressure of population.

The UK’s population had nearly stabilised in the Seventies and Eighties: birth and death rates were in balance, in some years more migrants leaving than arriving. There were even very small falls in population from 1975-78 and in 1982.

New immigration changed all that. Between 2013 and 2014, the population increased by 491,000 — one of the fastest rates of any industrial country.

That is not all. Women born overseas contributed 27 per cent of all live births in England and Wales in 2014, and 33 per cent of births had at least one immigrant parent — a figure which has more than doubled since the 1990s.

A post-Brexit government - such as one favoured by Boris Johnson - could decide to limit entry from the EU, possibly favouring highly skilled migrants

Taking into account many statistics, migration accounted overall for 85 per cent of population growth from 2001-2012.

This week, the Office for National Statistics (ONS) reported that the total number of EU nationals coming here under freedom-of-movement rules was 270,000 last year. This included a record number from Romania and Bulgaria. Overall migration, including those from outside the EU, was 333,000 in the year to December.

What, therefore, is the prospect for the future?

In none of the projections by the ONS does the UK population fail to grow to more than 70 million.

In the ‘Principal Projection’ (based on underlying assumptions of what is most likely to happen), the UK population (now 65 million) exceeds 70 million in 11 years, reaches 77 million by 2050 and exceeds 80 million by 2060. That implies an additional 2.9 million immigrants by 2030, not including their post-2014 children.

But these official assumptions are far below the actual level of recent net migration: 313,000 in 2014 and 333,000 in the 12 months to last December.

Were the 2014 actual inflow to persist, Britain’s population would exceed 80 million shortly after 2040, in 25 years’ time, and 90 million shortly after 2060.

Another measure is the number of new National Insurance numbers issued. These are given to EU citizens as a requirement to work here.

From 2011 to 2015, some 2,234,000 NI numbers were handed out.

That greatly exceeds the number of people who arrived from the EU in that period, according to the Office for National Statistics estimates.

This implies an undercount of 1.2 million, or about 240,000 per year. ONS has claimed that this is mostly accounted for by short-term migration, not included in the annual long-term migration figures.

Indeed, there are many reasons for supposing that net migration will not decline as the ONS assumes it will. On the contrary, it may even increase.

Any reduction in net migration to the UK requires at least one of the following developments:

Effective operation of the restrictions on welfare negotiated by David Cameron, which are subject to agreement of all the other 27 EU states — which could be problematic. Yet all commentators agree that the effects, even if they could be applied, would be nugatory.

A resolution of the euro crisis, and eurozone labour market reforms (so that youth unemployment in Greece, for example, falls from its current 49 per cent). Yet economic forecasts and the current outlook do not inspire confidence that such progress can be expected any time soon.

Convergence in real wages in Eastern Europe. Big wage differentials, not welfare, are the main attraction drawing East Europeans to Britain. At present, wages in their home countries are between one quarter and one-sixth of the UK level. Of course, the introduction of the National Living Wage here has further increased the attraction of the UK for migrants.

Further restrictions on the number of immigrants admitted from outside the EU. But this requires political will and judges to curb their activism in human rights cases — for example, further restrictions on the number of people allowed to come here to join their spouse, by increasing residence requirements, age limits on marriage, and proficiency in English language.

Ending employers’ dependency on migrant labour and persuading them to concentrate first on the domestic population for labour. Also, perhaps, an obligation to take on domestic workers in some proportion to overseas workers. The Government should moderate its own dependency on overseas labour, notably for the NHS.

UK exit from the EU. A post-Brexit government could decide to limit entry from the EU, possibly favouring highly skilled migrants. Indeed, there would be little point in Brexit without such measures. That would restrict EU inflows, most of which are in low-paid work.

Further expansion of the EU is likely to increase migration even more. The apparently relentless drive to the East by the EU Commission will activate further sources of migration as more poor countries are embraced by the EU. Looking to the future, citizens of possible new accession countries (such as Albania, Serbia, Macedonia, Montenegro, Turkey, Bosnia and Kosovo) will be eligible for work in the UK once they join.

The Prime Minister, pictured here with Tessa Jowell, is campaigning to Remain in the EU

The long-run migration potential from those countries is highly uncertain — but it is likely to be large. In case this seems fanciful, recall that an estimated one-third of the population of Albania is already thought to be living in Western countries.

Turkey is a special problem. It is not a European country, despite occupying a small corner of the European continent. Its accession would take the frontiers of the EU to those of Iraq, Iran and Syria.

Turkey’s population is 75 million and rising. Indeed, some of its regions are rock-bottom poor, with very high birth rates.

POPULATION CRISIS: FACTS AND FIGURES Between 2001 and 2014, 3.3 m migrants came to the UK Our population rose by 491,000 from 2013 to 2014 — one of the fastest rates of any industrial country Official projections suggest the UK population (now 65m) will exceed 70m in 11 years, hit 77m by 2050 and pass 80m by 2060 The cost of immigration between 1995 and 2011, according to a study, was up to £114bn Births in the UK rose from 668,777 in 2002 to 778,805 in 2013. Of these, births to immigrant mothers almost doubled from 110,484 to 196,806 Women born abroad contributed 27% of all live births in England and Wales in 2014, and 33% of babies had at least one immigrant parent 126,000 children of school age have come to the UK from the European Economic Area since 2004 Labour said 13,000 Eastern Europeans a year would come here. Yet 53,000 entered in the first year and 76,000 the next (both figures thought to be big underestimates) Advertisement

Repression of press freedoms and conflict with minorities — notably the Kurds — is becoming harsher. Despite that, the EU is being successfully blackmailed into accelerating Turkey’s stalled admission application in return for its help in the migration crisis. For his part, David Cameron remains in favour of Turkey’s admission to the EU, a position impossible to reconcile with his promises to reduce migration.

Certainly, Turkey’s potential for migration is very difficult to evaluate, but it is suggested that it would be about 100,000 per year to the UK. Why does all this matter?

Of course, the friends of population growth — Chancellor George Osborne, many in the Remain campaign, business periodicals such as The Economist and the FT — see no harm in it and much benefit. GDP and overall tax increase, they argue.

And, as the BBC and much of the media tell us, as immigration is good for the country, why complain?

One becomes weary of pointing out that GDP growth relates to the national economy as a whole and doesn’t benefit individuals.

A lso, there is the issue of those working in the black economy. It is impossible here to address adequately the arguments about the economic benefits of migration.

High-skilled migration is usually a benefit unless it generates dependency and deters domestic training and opportunity.

It is true that the immigrant contribution to most aspects of life in Britain will be apparent to everyone. It has brought many illustrious persons to Britain.

But on the simple fiscal calculations usually presented, the average benefits per capita are trivial and may be negative. In any case, the benefits of migration accrue mostly to the immigrant.

A study in 2014 which included some costs, such as education, as well as tax, earnings and benefits, showed that, overall, immigration from 1995 to 2011 imposed a total cost of between £32 billion and £114 billion, depending on the assumptions made — a positive contribution from European Economic Area migrants being greatly outweighed by the net cost of immigrants from the rest of the world.

Crucially, few of these fiscal calculations include the large additional costs imposed by migration: the need to build more schools, maternity wards and hospitals, and housing, the pressure on transport and infrastructure such as water resources. Immigrants bring no capital.

There is another key factor. Births in the UK have risen strongly since the beginning of the century; from 668,777 in 2002 to 778,805 in 2013. Of these, births to immigrant mothers have almost doubled from 110,484 to 196,806.

On top of that, the National Statistician (the Government’s principal adviser on official statistics) has disclosed that 126,000 children of school age came to the UK from the European Economic Area since 2004.

Schools are correspondingly under great pressure: 880,000 more pupils are officially projected by 2023, mostly as a consequence of immigration. Meanwhile, as immigration continues at a high level, most future housebuilding will be devoted to accommodating it. These facts are seldom raised when the housing crisis is discussed.

Diversity imposes costs, too, in new public sector bureaucracies, translators and legal complications.

Elsewhere, however much energy efficiency programmes may succeed in reducing energy demand, population growth puts pressure on energy adequacy. Maybe the lights will not stay on if today’s high migration levels persist.

Finally, immigration is making the most fundamental permanent change of all, in the composition of the population itself.

In the 1991 census, the non-white population, mostly of post-1960 immigrant origin, stood at 3 million or 6 per cent of the total in England and Wales. By 2011 this had increased to nearly 8 million, or 14 per cent of the total.

Those describing themselves as ‘White British’ comprised 88 per cent of the total population in 2001.

But by the 2011 census, the ‘White British’ population in England and Wales had declined by 400,000, whereas the non-white population had increased by over three million and the population describing itself as white but not British (many from Eastern Europe) had increased by just over a million.

So. What might the future hold for the ethnic composition of the UK?

I made a projection in 2010 that if immigration stayed at its long-term rate of around 180,000 a year as it was at the time, the White British-born population would decline from 80 per cent of the total then to just 59 per cent in 2051.

Taking the projection to a more uncertain distance, the White British population would cease to be the majority in the UK by the late 2060s.

However, should current high levels of immigration persist for any length of time, that date would move closer to the present. Britain would then become unrecognisable to its present inhabitants.

Some people would welcome a brave new experiment, pioneering a wider world future. Others, though, might say ‘Finis Britanniae’.

What does all this mean?

Some would welcome it as a move to a more diverse society. But as numbers in different groups increase, their need to integrate into British society becomes less and less, except inasmuch as they are needed to operate in the economy. And as the balance of numbers changes, the question arises as to who will adapt to whom.

Some, like many Pakistani Muslims in some Northern cities, continue to live a closed, traditional lifestyle in First World comfort, with little need to adapt to their British surroundings. Such groups increase, while UK space available to the White British diminishes.

The former head of the Equality and Human Rights Commission, Trevor Phillips, recently warned vigorously about the serious consequences of failing to adopt a strong policy of integration, warning of ‘squeamishness about addressing diversity risks allowing our country to sleepwalk to a catastrophe that will set community against community’.

The truth is that very high levels of immigration make this issue even more pressing than before.

I said at the start of this article that Britain is at a tide in its affairs.

If immigration is not substantially reduced, the country will be transformed out of recognition by the consequences of a very large population increase: schools, housing, environment, the make-up of the people of Britain, all will change in ways in which no one has been consulted and few want.

The coming referendum will not of itself resolve the issue. But it might offer the beginning of the end of an otherwise inexorable change.