A portrait of Britain in 2031

The causes of the relentless increase over the recent centuries in the UK's population – now projected to pass 70 million within 25 years – are many and varied.

They range from medical advances and growing individual prosperity to greater life expectancy and the waves of immigration.

The UK is now home to almost 61 million people, some 20 million more than a century ago and 50 million more than 1801, with the population growing in 99 of the past 100 years. Predictions that the number would stabilise at between 55 million and 60 million have been torn up and population growth is accelerating again, pushing the issue towards the top of the political agenda.

The rate of increase has even taken Whitehall's statisticians by surprise, with the Office for National Statistics (ONS) yesterday revising its population projections upwards. On current trends, the ONS now forecasts the numbers in Britain will grow to 62.8 million in 2011, 65 million in 2016, 67.2 million in 2021, 69.3 million in 2026 and 71.1 million in 2031, 78.6 million in 2051 and 85.3 million in 2081. That means that the UK's population is now rising by about 400,000 a year.

The face of Britain was transformed in the 19th century by the massive movements of people in the Industrial Revolution, and it will continue changing. Pressure for housing will mean swathes of countryside disappearing under concrete.

The country's demographic make-up is also altering rapidly, with Leicester set to become the first city where whites are in a minority by the end of next decade.

Just over half the population growth is caused by increases in family size – the average woman now has 1.84 children – and by greater life expectancy. Boys and girls born today will live an average of 77.2 years and 81.5 years respectively; that is forecast to rise to 82.7 years and 86.2 years for those born in 2031.

The rest of the growth has been driven by higher-than-expected levels of migration in recent years, with a net annual influx of about 190,000 compared with previous estimates of 145,000. Population increases are predicted for the whole of the UK, although they are expected to be smaller in Scotland than elsewhere.

The figures also confirm that a demographic time bomb is ticking, with the number of people over the state pension age – 11.3 million, and projected to reach 12.2 million in 2010 – for the first time exceeding the number of children.

The ONS stressed yesterday that, rather than making firm forecasts, its projections were based on current trends and that they became less reliable the further they looked into the future. Previous statisticians have got it spectacularly wrong when peering into the crystal ball. When the experts of the 1960s extrapolated the effects of the post-war "baby boom", they concluded that the population would be 75 million by 2007.

But Liam Byrne, the Immigration minister, said: "These projections show what could happen unless we take action now."

He said they underlined the need for "swift and sweeping" changes to the immigration system in the pipeline, including the introduction of an Australian-style points based system for migrants from outside the European Union.

The Tories are calling for annual limits on the numbers of new arrivals admitted into the country. David Davis, the shadow Home Secretary, said: "The shocking acceleration in the rate of population growth makes it more urgent than ever that the Government should introduce a properly controlled immigration system." Rosamund McDougall, of the Optimum Population Trust think-tank, said: "There is no parallel in our history for population growth of this magnitude. It will blow a massive hole in any national climate change strategy, impose huge strains on our infrastructure and environment, seriously damage quality of life and make Britain one of the most crowded and stressful places in the world."

A history of population growth

Pre-1300

Poor nutrition, famine and regular invasions kept Britain's population between two and four million for much of the first millennium of the Common Era. Average life expectancy was short, childbirth was deadly and making a living from the land precarious. Cities rarely comprised more than a few thousand people as the vast majority of the population lived in the country. London remained the only major city, with about 15,000 residents by 1100, growing to 80,000 by the late 14th century.

1300-1800

Britain's population was cut by successive waves of the bubonic plague, which first struck in 1348 and returned throughout much of the 14th and 15th centuries. The bacterial disease hit urban areas hard, killing 30,000 Londoners and wiping out between 30 and 50 per cent of the entire population. Disease caused by conflicts such as the Wars of the Roses and the English Civil War also hit numbers. Cities continued to grow but remained unpopular due to poor sanitation and living conditions.

1800–1900

During the 19th century, Britain experienced an unprecedented period of rapid population growth spurred on by the Industrial Revolution. As living conditions and health care improved alongside economic growth, Britain's population doubled every 50 years, from 10 million in 1801, when the first census was taken, to more than 40 million by the turn of the century. Industrial cities such as Manchester and Glasgow increased their population by a factor of 10 in just 100 years.

20th Century

Although Britain's population continued to expand throughout the 20th century, the rate slowed down from the phenomenal explosion seen during the previous century. The First World War and the flu epidemic that followed heralded a drop in the population from 45 million in 1911 to 42 million 10 years later. The decades following the Second World War saw a large increase in the UK's population as migrants from the West Indies and the Asian sub-continent flocked to Britain to find work.