The Big Question: Is Britain going to be able to support an ever-expanding population?

Why are we asking this question now?

The annual Social Trends study published earlier this week by the Office for National Statistics states that the number of people in the UK is growing by 1,000 a day. There are 61 million people officially resident in Britain today and this is expected to grow by 4.4 million by 2016.

If past trends continue, the office predicts that there will be 71 million people living in the UK by 2031. Longer-term projections suggest that Britain could have 85 million inhabitants by 2081, and possibly 100 million by 2100 if current increases continue unchecked.

Most of the increase in numbers over the next 20 to 30 years will be due to net inward migration – more people coming to live here than leaving the country to live abroad – and longer lifespans, rather than an increase in the birth rate. However, although birthrates have fallen over the past few decades, they have increased again in recent years, mostly due to the higher birthrates of new immigrants.

What does an extra 10 million UK residents mean?

The number is equivalent to about 55 towns the size of Luton, which has a population of 184,000, or a megacity that is 1.5 times the size of London. It will mean extra housing, schools, roads and other building infrastructure. It will put further pressure on open countryside, water resources – which are already in short supply in the South East – and hamper efforts to meet Britain's targets on cutting carbon dioxide emissions. A 10 per cent increase in the population of Britain in such a short period of time would have a huge impact, especially in those parts of the country where most of the new residents will want to live – London and the South-east.

How does this future increase compare with past increase in the UK population?

The number of people in Britain has grown sixfold since 1800 and by more than 20 per cent since 1950. However, since the 1960s, a decline in the birthrate led to a fall in the rate of increase in the population, which has been reversed in recent years. In 2007 alone, the UK population increased by 434,000 people, enough to fill a city the size of Cardiff.

England has about 50 million residents, making it the fourth most densely populated country in the world – with almost 1,000 inhabitants for every square mile – if small island nations and city states are excluded. England is even more densely populated than Japan.

Does the Government have a policy on population?

Not really, although in October 2008 the new immigration minister Phil Woolas said: "This Government isn't going to allow the population to go up to 70 million." However, the Government has not spelt out how it is going to prevent a growth in human numbers, a growth that it has in the past welcomed on the grounds that an ageing population needs an army of young immigrants to keep them in the lifestyle to which they have been accustomed. This policy of encouraging net immigration to relieve the "timebomb" of an ageing population has also been criticised by demographers who point out that the policy is unsustainable – young immigrants ultimately get old too.

What is the global situation regarding human numbers?

The current global population stands at about 6.5 billion and this is expected to grow to about 9.4 billion by 2050. What happens after that is debatable. Some projections suggest it could remain stable or even decline slightly towards the end of the century. Other studies suggest that the global population could continue to rise to as much as 12 billion by 2100. A fall in numbers in some parts of the world will be offset by a rapid rise in other regions, notably sub-Saharan Africa and the Indian subcontinent.

Is anyone worried about the growth of the human population?

For years, indeed decades, population was "the elephant in the room" for the environmental movement, which was scared of raising the issue for fear of causing offence, particularly in the developing world. However, an increasing number of high-profile people are putting their heads above the parapet and the subject of human population is now less of a Cinderella subject than it once was.

The latest campaigner is Sir David Attenborough who last week announced that he has become a patron of the Optimum Population Trust, a leading think-tank in the subject. Sir David said that the global explosion in human numbers is putting mounting pressure on wildlife and the environment. "I've never seen a problem that wouldn't be easier to solve with fewer people, or harder, and ultimately impossible, with more," he said.

Other well-known figures to voice their concerns over the growth of human numbers include the environmentalist Jonathan Porritt, the Earth scientist James Lovelock and Chris Rapley, the director of the Science Museum in London.

Lovelock and Rapley have long advocated a wider debate on human numbers, arguing that the planet just cannot support its present population, let alone the one it will grow to in 2050 if left unchecked.

Is there an optimum human population and what is it?

This comes down to the "carrying capacity" of the planet, in other words how many people it can comfortably support sustainably. Another way of looking at the problem is to ask how many "earths" are needed to support the present population of 6.5 billion people. Some researchers have suggested that we are currently using up the natural resources of between 1.2 and 2 planets. But there are still some 800 million people or more currently suffering from hunger and malnutrition. If everyone on the planet were to enjoy an American lifestyle, for instance, we would need about 13 planets. This is equivalent to saying that one Earth could support about 450 million people.

Obviously, we do not need to live like an average American to have a comfortable lifestyle, so it is possible for the Earth's capacity to support more than 450 million people. But the ultimate size of the optimum global population is debatable, with some putting it at about 1 billion people and others suggesting a higher figure of about 2.5 billion or more. Few experts believe that the present global population is sustainable, never mind the population that is expected to exist by 2050.

Why should a growing human population matter?

It comes down to what Thomas Malthus stated nearly two centuries ago. Human numbers grow exponentially – at an accelerating pace – if left unchecked, while resources and food grow in a slower, linear fashion. The exponential growth of human numbers will therefore outstrip food and resources without a constant series of miracle "green revolutions" that can feed a growing world. In other words, an expanding human population will ultimately lead to hunger and starvation without it being controlled.

Should the UK have a policy on population?

Yes...

* The growth in the UK population is environmentally unsustainable

* Britain is a small island and there is limited space for new housing and the infrastructure needed to provide more people

* Policies on climate change will not work if we continue to allow the population to increase unchecked

No...

* We need a growing population to support an increase in the number of older people who can no longer work

* More young people are essential to keep the country vibrant, innovative, and economically prosperous

* A population policy will only be used to impose draconian measures to limit future immigration