The population of the UK increased by more than half a million in a year, official estimates have revealed.
Natural growth - more births than deaths - of 171,800 and net international migration of 335,600 helped push the number of people living in the country to 65.1 million as of the middle of 2015.
This was an increase over the year of 513,000, or 0.8%. The Office for National Statistics said the rise was similar to the average annual increase seen over the last decade.
Population change due to the difference between births and deaths is at its lowest level since the year to mid-2006.
The ONS said: "The number of births has decreased on last year's figure and is below the average for the period, while there was an increase in the number of deaths since last year, partly attributed to flu outbreaks in early 2015."
Meanwhile, an increase in immigration (up 53,700) and a smaller decrease in emigration (down 22,300) have both contributed to the increase in net international migration compared with that seen in the year to mid-2014.
Net international migration in the year to mid-2015 was at a similar level to that seen a decade earlier, the ONS said.
"This is caused by a combination of more people arriving to stay in the UK and fewer people leaving the UK on a long-term basis," its report said.
International migration inflow is at its highest since the year to mid-2007, the ONS said, while outflow is at its lowest since comparable records began in 2002.
The figures indicate that migration accounted for just under two-thirds (65%) of the annual change.
In addition to the direct impact on the size of the population, current and past international migration also has indirect effects on the size of the population as it changes the numbers of births and deaths in the UK, the ONS report said.
The figures were released hours after the polls opened in the EU referendum and come after a campaign which has been dominated by debate over immigration.