The UK population grew by almost half a million last year to 64,596,800,according to figures from the Office for National Statistics.
The “above average” increase of 491,100 from mid-2013 to mid-2014 included net migration adding 259,700 to population growth, the ONS figures show.
This was more than “natural growth” – births minus deaths – which added 226,200.
The ONS said a quarter of births were to mothers born outside the UK.
The overall number of births was down compared with the previous year, continuing a downward trend seen since a peak in mid-2012.
The population increase was above average compared with rises over the last decade, the ONS said.
As well as net migration and natural growth, other changes and adjustments, mainly in the armed forces, accounted for an increase of 5,200 people, the ONS said.