The population of the U.K. will jump by almost 10 million over the next 25 years, according to official estimates.
More than two thirds of the projected rise from 64.6 million in mid-2014 to 74.3 million in 2039 is due to assumed net migration and the indirect impact of people arriving on the birth rate, the Office for National Statistics (ONS) said.
It means that over the next quarter of a century the number of people in the country is set to increase by the approximate equivalent of the current population of Sweden.
The ONS also said the population is projected to reach 70 million by mid 2027, while it will rise by 4.4 million over the next decade.
Statisticians also projected that Britain's society will continue ageing, with more than one in 12 people aged 80 or over by 2039.
By 2024 the UK's population will increase by the equivalent of about the current size of Ireland, the figures suggest.
The data is published every two years. Compared to the last set of figures, which were based on 2012 estimates, experts have raised the projected growth over the next 10 years by just under a quarter of a million.
The average annual growth rate of 440,000 in the first decade means the population will rise by more than the number of people currently living in Dorset each year.
Britain's estimated growth outstrips the Europe, with the country's population estimated to increase by 15% in the next 25 years compared to 3% in the EU.
Only Luxembourg, Belgium and Sweden are individually expected to see larger rises, although the projections for Europe were based on figures compiled prior to the recent migrant crisis.
On current trends the UK will overtake France by 2030 and Germany, becoming the largest country in Europe, by 2047.
Guy Goodwin, director of social analysis at the ONS, said: "The UK's population is set to grow and age.
"Growth will be at a faster rate than we have seen previously, largely due to the direct impact of international migration and the indirect impact of immigration.
"Despite this, the population will also be older as those born shortly after World War Two and during the 1960s 'baby boom' reach the oldest and pensionable ages respectively.
"The number of people of age 80 or over will more than double over the next 25 years."
The figures are used to inform policies on pensions, migration and care, as well as the planning of housing and services.
Statisticians said the assumed average annual net migration - the difference between the number of people arriving and leaving - was 198,000 over the 25 year period.
The most recent estimate showed net migration stood at a record 330,000 in the year to March.