The UK's population is at a record level after it increased by almost half a million to 64.6 million within a year, according to official figures.
The increase between mid-2013 and mid-2014 included net immigration of 259,700, the Office for National Statistics said.
Over that period 582,600 migrants arrived in the UK, compared with 322,900 people leaving the country - accounting for 53% of the increase.
Net international migration was the highest since the year to mid-2011 and up by 76,300 from 183,400.
An ONS spokesman said the statistics showed the UK population had grown by almost half a million since mid-2013, up 0.77% to 64,596,800 - higher than the annual increase of 0.75% over the last decade.
The estimated population of England in mid-2014 was 54.3 million, up 0.84%, with the corresponding figures for Scotland standing at 5.3 million (up 0.37%), 3.1 million in Wales (0.31%), and 1.8 million in Northern Ireland (0.59%).
The overall increase was due to natural growth of 226,200 and a net migration of 259,700, while an increase of 5,200 was due to other changes and adjustments, mainly in the armed forces.
Over the period, the median age of the population was 40, the highest ever estimated, with the proportion of older people continuing to rise with more than 11.4 million people aged 65 and over, up from 11.1 million the previous year.
Projections from the ONS indicate that by 2044 a quarter of the UK population will be aged 65 and over.
The trend of an ageing population has continued over the last 30 years, partly due to an increase in life expectancy and also the high number of births in the years following the Second World War.
Campaign group Population Matters, which carries out research on the environmental impact of population size, said the growing population is having an effect on the quality of life and that it is time to address the "population problem".
Simon Ross, chief executive of the organisation, said: "The world is heading for an additional four billion people by 2100. The ONS estimates should serve as a warning that we need to act sooner rather than later to reduce population growth.
"We are all affected adversely by the rapid population growth of recent decades. Examples include pressure on housing and public services to the environment and climate change.
"As a nation we need to invest more in addressing these issues. Our emphasis should be on improved family planning and women's education and empowerment, together with public information campaigns about the immense strains population and consumption growth place on our planet."
He added that the Government needed to talk about family planning as part of a sustainable lifestyle, and look at ways of keeping the older population in work.
Mr Ross said: "The Government and employers need to work together to help people stay in work longer - older people have got great experience, and a lot of work can be done from home.
"We need to work to keep hold of people contributing, and in work."
He emphasised that the growing population is "creating a housing crisis, it is contributing to rising energy costs, it is creating issues like people not being able to see their GP", and called for people and those in the public eye to talk more openly about having smaller families.
Mr Ross said: "There has been a history of not talking about it. They should be saying, 'I am having a smaller family because I am concerned about the future of the environment, and I am concerned about sustainability'.
"More celebrities should be saying that they are having smaller families because they are worried about the future of the planet."