Stats published today showed the mid-year estimate for the UK's population growing by 513,200 to reach 65.1m.
The growth is equivalent to a city of the size of Manchester - defined at 503,127 in the 2011 Census.
It is only the third time the estimate has increased by more than 500,000, and the second largest increase on record.
The figures include long-term international migrants who have changed their country of residence for 12 months or longer, but do not include people who leave the country within a year.
The growth was driven by both an increase in net migration, recorded at 335,000 in the most recent figures, and a 171,100 rise in “natural growth” – births minus deaths.
The figures also showed the number of births had decreased, falling below average, while there was an increase in deaths last year, partly due to flu outbreaks.
There were increases across England, Scotland, Wales and Northern Ireland, but the biggest growth was in England, its population climbed by 469,700 to 54.8m.
By contrast, the mid-year estimate for Wales' population climbed just 7,100 to 3,099,100.
The median age of the UK population at mid-2015 was 40, this increase is higher than the median age of 38.7 in mid-2005.
While the populace was estimated at 49.3 per cent male (32.1m people) and 50.7 per cent female (33m), meaning there are 103 women for every 100 men, slightly down from 105 in mid-2005.
This is in part, a factor of the increasing numbers of men living beyond 85, which has increased by more than half over the last ten years, compared to a 21 per cent increase in the numbers of women.
The ONS attributed the change to reductions in smoking numbers, advances in health treatment for circulatory diseases and male occupations becoming less physical and safer.