Our exploding population is the gravest threat Britain faces today



Overpopulation brings longer hospital waiting lists, crowded trains and unaffordable housing



For most of my professional life, I have derided the population alarmists. Those who spent the past few decades warning that there were far too many people in Britain and the wider world had always struck me as shrill, their arguments flawed at best and downright racist at worst.



Back in the Seventies, it was received wisdom that, by the early 21st century, the West would be groaning under the weight of its billions, with famine stalking the land and supermarket shelves empty.



This didn't happen. Instead we face an obesity epidemic, and, in the rich world, ageing populations which - we are told - have to be shored up by mass immigration.



So why have I changed my mind? Why do I now agree that excessive human population is not one of Britain's biggest problems but, arguably, the greatest single threat to health, wealth and well-being we see in the world today?



First, let me be clear: this is about cold, brute numbers and not at all about race, culture, ethnicity nor any of the other inflammatory issues which have clouded the great population debate.



The problems of overpopulation are caused by too many people - full stop. Not by too many Ghanaians or Kenyans, not too many Poles or gypsies, not too many of any other particular kind of people - just too many people of all colours, creeds and cultures.



It is now hard to think of a single major problem we face, here in Britain or elsewhere, which would not be solved, or at least ameliorated, by having fewer people.

Yet Home Secretary Alan Johnson yesterday ruled out imposing a cap on immigrant numbers, saying he didn't 'lie awake at night worrying about a population of 70 million'.



He told the Commons Home Affairs Committee we should 'welcome' immigrants who came to live and work here, and that he was 'happy' to live in a multicultural society.



Where on earth has Mr Johnson been these past few years? Everywhere you look, the problems of overpopulation are becoming ever more apparent.



Everything from hospital waiting lists, crowded trains, the looming energy crisis, water and sewer systems unable to cope, unaffordable housing and unavailable dentistry have, at their core, Britain's burgeoning population.



Officially, the UK's population stands at around 61 million, although the true figure is almost certainly a couple of million higher - a legacy of the poll tax days when many people did not want to be counted on official censuses, and also of the fact that hundreds of thousands of foreigners are living here illegally and also do not wish to be counted.



And Britain's population is rising, with one of the fastest growth rates in the developed world. A new study published this week points out that by 2029 there will probably be 70 million people in Britain, with nearly all the extra people living in England, which is already the most crowded part of Europe. And most of this projected population increase will be driven by immigration.



On a purely economic basis, this can be a good thing. Certain national fixed costs, such as defence, the BBC, major infrastructure projects such as new railway lines and so on, are shared among more people and hence become, per head, cheaper.



Moreover, immigrants are for the most part young, fit and driven. They want to work, to get rich and to make a better life for themselves. Provided they come here legally and integrate, they contribute to the economy through their taxes, as well as helping to make Britain a more vibrant place in which to live.



It is no surprise that in the UK, as in other countries, cities which have attracted the most immigrants in recent years tend to be more cosmopolitan, richer and more interesting for it.

Compare thriving, vibrant London and Los Angeles with stagnant Detroit and Sunderland, once-thriving cities which have static or falling populations.



But there is a price to pay.



Although fixed costs might drop, per person, there is no doubt that as the south of Britain in particular becomes more crowded, many things that come under the heading 'quality of life' will become steadily worse.



Our roads will become even more congested, our trains more crowded and even slower, the waits for service longer and delays ever more a part of life.



Housing will become ever more unaffordable, we will have to spend billions on new schools and hospitals to cater for the equivalent of two new Londons - two vast metropolises somehow to be shoehorned into what is already a desperately crowded land.



We will, inevitably, lose great swathes of our countryside. The green belts will have to disappear. Ghastly and ill-conceived 'new towns' will spring up all over the South East and Midlands, the areas where new people want to live. London and its environs are already, effectively, full; but that will not stop them getting fuller still.



One result of all this is that Britain will miss all our environmental targets by a long mile. The Government is committed to reducing our greenhouse gas emissions by 60 per cent of 1990 levels by 2050.



This is going to be hard, if not impossible, with an extra ten to 15 million people - something hardly ever mentioned by the climate change brigade.



Supporters of mass immigration are fond of talking about the 'support ratio' - basically the number of people of working age for each person aged 65 or older.



As more and more people live longer, and as the number of babies born continues to fall, we will need, we are told, mass immigration to keep the ratio at current levels - about 4:1



But this is a desperately flawed thesis. For it ignores a rather obvious fact that today's young eager working immigrants will, of course, become tomorrow's elderly and dependent population.



As Oxford University demographer Professor David Coleman says: 'If you rely on mass immigration to maintain the support ratio, you end up with a huge acceleration in population growth.'



Indeed, according to one study, we would need to increase Britain's population to 300 million by the end of the century to keep the numbers balanced. Ridiculous. So what is to be done?



For a start, we will have to forget about maintaining the current support ratio - a legacy of the days when people died younger and had more children. This means we will have to accept later retirement and a generally older population.



In Britain, we will also need a policy of controlled migration - ideally one which aims to balance emigration with immigration (which happened, naturally, well into the Eighties). That alone, coupled with our rather low birthrate, would see the UK's population falling by several million by late-century, rather than increasing by a third.



As I said, this is not an argument about what kind of people we are, just raw, brute numbers.



And globally? Here the prognosis is rather gloomy. Across a vast swathe of Africa and south-west Asia, population growth is now at historically unprecedented levels.

Countries such as Nigeria, Ethiopia, Somalia, Pakistan and Yemen are set to triple, quadruple and quintuple their populations in the coming century.



Nothing short of a global catastrophe will stop the world's population peaking at about nine billion by 2050 or so. That's the equivalent of an extra two Indias. And all of these new people will add hugely to pressures on housing, greenhouse emissions, food, water and transport.



Like it or not, the world of the near-tomorrow - despite Home Secretary Alan Johnson's blithe rejection of the idea - is going to be an intolerably crowded version of the world of today.



The solution, in the third world, lies with educating women and girls, and giving them full economic and reproductive rights. Where this has happened, as in south-east Asia, spiralling population growth rates were stopped in their tracks.



Most of all, we are going to have to start talking about all this before it's too late. In Britain, we might lose our green belts, but Africa may well lose all its wildlife and forests - and face mass famine - if we do not tackle this problem soon.



The 21st century is make-or-break for us and our planet. It would be a tragedy if population growth became a catastrophe - a catastrophe we were too polite to even mention.