The UK population could reach 72.5 million by mid-2032, up from the latest estimate of 67.6 million, driven almost entirely by net migration, figures suggest.
The Office for National Statistics (ONS) projects an increase of 4.9 million (7.3%) from net migration, compared with 6.8 million births and 6.8 million deaths.
The data, published on Tuesday, assumes a level of long-term net international migration of 340,000 a year from mid-2028 onwards.
James Robards, from the ONS, said: "The UK population is projected to grow by almost 5 million over the next decade. The driver of this growth is migration, with natural change - the difference between births and deaths - projected to be around zero. These projections are based on current and past trends, and aren't forecasts about what may or may not happen in the future.
"Our latest projections also highlight an increasingly ageing population, with the number of people aged over 85 projected to nearly double to 3.3m by 2047. This is in part because of the ageing of the baby boom generation, as well as general increases in life expectancy."
Conservative shadow home secretary Chris Philp described the projection as “shocking and unacceptable”, adding: “It can and must be stopped from materialising” as he called for a “hard binding legal cap on visas issued each year”.
The overall population of the UK is projected to rise by 7.3% between mid-2022 and mid-2032, compared with an increase of 6.1% over the previous 10 years.
England's population is projected to grow more quickly than other UK nations in the decade to mid-2032, increasing by 7.8%, compared with 5.9% for Wales, 4.4% for Scotland and 2.1% for Northern Ireland.
The ONS also provides a projection further into the future, covering the 25 years between mid-2022 and mid-2047, for which the total projected growth of the UK population is 8.9 million, a jump of 13.2%.
This is lower than the previous 25 years from 1997 to 2022, when the population is estimated to have risen by 9.3 million, or 15.9%.
The number of people at state pension age is projected to rise by 1.7 million between mid-2022 and mid-2032, up from an estimated 12.0 million to 13.7 million people.
This projection accounts for the planned increases in state pension age to 67 for both sexes.
Meanwhile, by mid-2032 more than one in 10 (10.3%) of the UK population are projected to be aged 75 and over, compared with about one in 11 (9.1%) in mid-2022.
The ONS stressed the figures are projections - not predictions or forecasts - because they are based on current and past trends and there is always a level of uncertainty over how the numbers could change as time goes on.
