The latest calculations reveal there was an estimated 66,436,000 people living in the country at the end of June last year, according to data from the Office for National Statistics (ONS).
But the growth rate remained the same as the previous year.
Over the 12 months to the middle of 2018, the UK population rose year-on-year by 0.6%, with the annual growth rate remaining slower than any year since mid-2004.
Scotland's growth rate is slower than any other nation or region in the UK, with the population having risen by just 13,300 (0.2%) to 5,438,100
Neil Park, head of the ONS population estimates unit, said: "For the fifth year in a row, net international migration was a bigger driver of population change than births and deaths.
"However, overall population change to the year mid-2018 has remained fairly stable as an increase in net international migration has been roughly matched by the fewest births in over a decade and the highest number of deaths since the turn of the century."
The figures also show the number of births in the year to mid-2018 was 744,000 - the fewest in any year since 2006, and down 2% on the previous 12 months.
By contrast the number of deaths rose 3% to 623,000 - the most since the year 2000.
It means natural change in the UK population - the number of births minus the number of deaths - is now at its lowest level since 2004.
Net international migration in the year to mid-2018 was 275,000, which was "broadly in line" with the average of the last five years, the ONS said.
The four local authorities with the fastest-growing population are all in central London.
The "relatively high level" of population growth in the City of London, Westminster, Camden and Tower Hamlets is "partly a reflection of the increase in net international migration" between mid-2017 and mid-2018, the ONS added.
Robin Maynard, of charity Population Matters, said: "These figures give no grounds for complacency about UK population growth.
"Birth rates and migration fluctuate from year to year but our already unsustainable population is continuing to rise and that will continue until a positive strategy is put in place to address it.
"The Government has announced ambitious plans to achieve a zero-carbon economy but by ignoring our unsustainable population growth, it is driving with the brakes on.
"More people means more emitters and more emissions.
"Our growing numbers are incompatible with our climate change commitments, the health of our environment and our quality of life."
Laura Gardiner, research director at the Resolution Foundation think tank which aims to improve the standard of living, said: "The UK population is ageing particularly fast at the moment because rising life expectancy is being amplified by the large baby boomer generation moving from working age into retirement.
"But the rates of change vary greatly across the country.
"The large share of pensioners across some coastal parts of the country stands in stark contrast to far younger populations in Britain's major cities.
"This has huge implications for public service provision across the UK, and how those services are funded."
UK POPULATION ESTIMATES BY NATION AND REGION
Here is a full list of 2018 population estimates for the nations and regions of the UK, including the change on 2017.
South-east England: 9,133,625 (up 52,800 or 0.6%)
London: 8,908,081 (up 83,080 or 0.9%)
North-west England: 7,292,093 (up 33,466 or 0.5%)
Eastern England: 6,201,214 (up 32,782 or 0.5%)
West Midlands: 5,900,757 (up 40,051 or 0.7%)
South-west England: 5,599,735 (up 40,419 or 0.7%)
Yorkshire & the Humber: 5,479,615 (up 29,485 or 0.5%)
Scotland: 5,438,100 (up 13,300 or 0.2%)
East Midlands: 4,804,149 (up 32,483 or 0.7%)
Wales: 3,138,631 (up 13,466 or 0.4%)
North-east England: 2,657,909 (up 13,182 or 0.5%)
Northern Ireland: 1,881,641 (up 10,807 or 0.6%)