LONDON - The population of Britain reached 64.6 million, increased by almost half a million within a year, local authorities announced Thursday.

Office for National Statistics (ONS) on Thursday published the Annual Mid-year Population Estimates of Britain in 2014, showing that the population in Britain in June 2014 reached 64,596,800, increasing by 491,100 from June 2013.

Statistics from ONS showed the increase included 226,200 natural growth, which means 777,400 babies were born while 551,200 people died in the 12 months; and 259,700 net international migrants, as 582,600 international migrants arrived in Britain and 322,900 left.

ONS said the number of births in the past year to mid-2014 declined comparing with the previous year, while the net international migration witnessed the highest level.

The median age of the population at mid-2014 was 40 years, the highest ever estimated, it said.

New statistics also exposed the pressure of graying society of Britain, as the population of people aged 65 and over reached 11.4 million in mid-2014, accounting for 17.7 percent of the country's population.