UK population increases by 400,000
The UK's population increased by around 400,000 to more than 64 million in the year to mid-2013, according to the latest official figures.
The Office for National Statistics (ONS) said the difference between the number of births and deaths during the year had contributed slightly more to the rise than migrants coming to Britain.
While there were 212,100 more births than deaths between mid-2012 and mid-2013, the figures show 183,400 more immigrants arriving in the UK than emigrants leaving.
An ONS spokesman said the statistics meant the UK population, which now stands at 64.1 million, has increased by around five million since 2001, and by more than 10 million since 1964.
Last year's growth, slightly below the average seen over the previous decade, means the estimated population of England in mid-2013 was 53.9 million (up 0.70%).
The corresponding figures for Scotland stand at 5.3 million (growth of 0.27%), compared to 3.1 million in Wales (growth of 0.27%) and 1.8 million in Northern Ireland (up 0.33%).
ONS estimates also showed the population of the UK had risen by more than the average seen across the European Union, exceeding the growth rate experienced in its four most populous members states.
Commenting on the statistics, monitoring group Migration Watch UK said a rise of 400,000 in a single year was the equivalent of adding two cities the size of Portsmouth to the population.
Alp Mehmet, vice chairman of Migration Watch, described the growth as "clearly unsustainable" and claimed it raised serious questions about the ability of public services and infrastructure to cope.
"The Government will have to build schools, GP surgeries, hospitals and homes as well as expand an already creaking infrastructure in order to cope with this demand at a time when there is very little money to spare," Mr Mehmet said.
Campaign group Population Matters, which carries out research on the environmental impact of population size, said Britain's continued growth was affecting living standards, particularly in London and the South East of England.
Its chief executive, Simon Ross, said: "Economic growth does not improve living standards if the benefit has to be spread across ever more people and if rising demand increases the cost of living.
"We would all be better off with a stable or falling population.
"We call on the Government to acknowledge this and make smaller families and balanced migration explicit goals."