Britain's population will surge past 70 million before the end of the next decade, new forecasts reveal today with more than half the increase caused by immigration.

The number of people living in Britain will rise by 3.6 million - 5.5 per cent - in a decade and the country will be home to 70 million by mid 2029.

The new forecast from the Office for National Statistics considers immigration, fertility and life expectancy.

It concluded that over the next ten years, 46 per cent of UK population growth is projected to result from more births than deaths, with 54 per cent attributed to net international migration.

Taking into account babies born to foreign parents in Britain, immigration will indirectly account for 77 per cent of the population growth.

The most recent set of immigration statistics showed net migration in the year to March 2017 was 246,000 - including 127,000 arrivals from the EU, 179,000 from the rest of the world and 60,000 people leaving the country.

Downing Street said the figures were only a projection but said it showed the Government was 'right to continue work to get migration down to sustainable levels.'

Overall, the population is expected to grow more slowly than at the last forecast in 2014 because of lower immigration, women having fewer children and a slow down in the growth of life expectancy.

Britain's population will surge past 70 million before the end of the next decade, new forecasts reveal today with more than half the increase caused by immigration

The number of people living in Britain will rise by 3.6 million - 5.5 per cent - in a decade and the country will be home to 70 million by mid 2029

Lord Green of Deddington, Chairman of Migration Watch UK, warned the projections were 'extraordinarily low' based on historical migration

Over the decade from mid-2016, the projections suggest that 7.7 million people will be born and 6.1 million will die, while 5.2 million people will immigrate on a long-term basis to the UK with 3.2 million emigrating from the country.

WOMEN HAVING FEWER BABIES SLOWS POPULATION GROWTH Women are having fewer babies meaning the population is growing more slowly than thought, the ONS said today. Over the next decade, statisticians expect 7.7million people to be born in Britain. As well as the direct impact, international migration has an indirect impact on the population in terms of its effect on the numbers of births and, to a lesser extent in the shorter term, deaths. For example, women immigrating to the UK who subsequently have children will increase the numbers of births. Advertisement

Lord Green of Deddington, Chairman of Migration Watch UK, warned the projections were 'extraordinarily low' based on historical migration.

He said: 'This is serious because it will lead to inadequate planning for housing, schools, hospitals and infrastructure – as, indeed, we have seen in recent years. Yet again the ONS have been much too cautious.

'It is also of note that, on the principal projection, immigration, including the effect on births, will account for 77 per cent of population growth over the next 25 years.

'If immigration continues at the ONS high migration assumption, which is roughly present levels, the population will grow by almost ten million, of which 82 per cent will be due to immigration – that is an additional eight million people.

'This underlines the need for a successful Brexit which could substantially reduce recent levels of net EU migration, perhaps by 100,000 a year.'

Andrew Nash, of the ONS Population Projections Unit, said: 'Over the period between mid-2016 and mid-2026 the population of the UK is projected to grow from 65.6 million to 69.2 million, reaching 70 million by mid-2029.

The shape and make up of the UK population will change dramatically by 2041. The current population is shown in the dark bars with men on the left and women on the right. The forecast for 2041 is shown in the lighter bars, showing fewer young people and more older people

'England is projected to grow more quickly than the other UK nations.

'Over that period 54 per cent of growth is projected to result directly from net international migration.

'The other 46 per cent is because there will be more births than deaths.

'These projections suggest slower growth than the previous (2014-based) projections.

'This is because of lower assumptions about future levels of fertility and international migration, and an assumption of a slower rate of increase in life expectancy.'

The study also gives a fresh indication of the ageing nature of the population.

It says the proportion of people aged 85 and over is projected to double over the next quarter of a century.

The total projected increase in the number of residents in the UK over the next 25 years is lower than that over the previous 25 years, the report notes.

The study also gives a fresh indication of the ageing nature of the population. In 2041 (blue bars) there will be almost the same number of children as today (red bars) but far more pensioners

Between mid-1991 and mid-2016 the population grew by 8.2 million (14.3 per cent) while between mid-2016 and mid-2041 it is projected to grow by another 7.3 million (11.1 per cent).

LIFE EXPECTANCY IS RISING SLOWER THAN THOUGHT Life expectancy is rising slower than expected, cutting the rate of population growth. The share of the population made up by older people is still growing and the population will continue to get older overall. The ONS is no longer assuming a faster rate of increase in life expectancy for those born between 1923 and 1938. By mid-2041 there are projected to be many more people at older ages. This partly reflects the 1960s baby-boomers now being in their 70s, but also the continued increase in life expectancy meaning that more people live to very old ages. Advertisement

Over the decade from mid-2016 projected growth varies substantially between the four nations of the UK.

England's population is projected to grow 5.9 per cent over this period. For Northern Ireland the figure is 4.2 per cent while for Scotland and Wales the figures are 3.2 per cent and 3.1 per cent respectively.

As well as the direct impact, international migration has an indirect effect on the population, statisticians said.

For example, women coming to the UK who subsequently have children will increase the numbers of births.

Conversely, women emigrating before they have children will decrease the number of births.

Once the indirect effect is taken into account, international migration accounts for more than three quarters (77 per cent) of the projected UK population growth over the 25 years from 2016, according to the ONS report.