The UK's overall population is set to reach 73m people by 2037 with the number of people aged 80 and over set to double, according to an ONS report.

The 2011 census put the UK population at roughly 63m, which means that the projected 2012 figure would represent a relatively gradual growth of 15% in 26 years.

The projection also suggests that the UK's population will increase past 70m in 2028.

The figures have been revised very slightly downwards from the 2010 projections. For example, the total population projected for mid-2022 is expected to be 0.2% lower than in the 2010 attempt.

An ageing population

Older people are going to make up a much larger proportion of the UK population in the future. The number of over 80s is set to more than double from 3m in 2012 to 6.1m in 2037.

The proportion of the UK population aged 75 and over will grow from 7.9% in 2012 to 13% in 2037. This will have the effect of driving the average age of someone in the UK up from 39.7 years in 2012 to 40.6 years in mid-2022 and 42.8 years by mid-2037.

The figures also show a 31% growth in the number of people of state pension age putting it up to 16.1m in 2037.

What will drive the growth?

57% of the projected 9.6 million population increase over the next 25 years is set to be driven by "projected natural increase", which essentially means there being more births than deaths.

The remaining 43% will be down to migration but, of course, people migrating to the UK also have an affect on the birth rate. Higher migration means more people of child-bearing age will be in the population.

29% of the 5.4m projected natural increase in the population size between 2012 and 2037 will be partially down to migration.

The figures are skewed quite heftily the other way in Scotland where 72% of the 206,000 projected increase in population over the next decade will be due to migration.

What if the projections are wrong?

The ONS has accounted for several different variables in their projections. Say, for example, that there are higher than projected levels of migration the population could increase to 74m instead of 73m people by 2037.

Under the highest projection, assuming high fertility, high life expectancy and high migration, the UK's population will reach 78m in 2037 while under the lowest, with all those things at lower than expected levels, the population will only grow to 68m.

To show how those figures break down the ONS have created an animated interactive showing how population pyramids will change over time if the variables alter.

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