The UK population has hit 66.4 million, according to the Office of National Statistics.
It said that an estimated 66,436,000 people were living in the country at the end of June.
The growth rate remained the same as the previous year at 0.6 per cent, which marks the slowest rate of growth since 2004.
ONS spokesman Neil Park said: “For the fifth year in a row, net international migration was a bigger driver of population change than births and deaths.”
He said the stable growth rate is due to an increase in migration matched by a low birth rate and the highest number of deaths since the turn of the century.
The number of people aged 85 and over is projected to double over the next 25 years.
By 2026 the UK population is projected to reach 69 million people, with the majority of this growth expected to come from international migration.
The latest migration figures from show that in 2018 around 602,000 people moved to the UK, while 343,000 left.
Long-term immigration from EU countries has fallen since 2016, and is at its lowest since 2013.
However non-EU immigration has gradually increased during that time.