More babies were born in the UK in 2011-12 than any year since 1972, the Office for National Statistics says.
In all, 813,200 UK births were recorded in the year, said the ONS, contributing to population growth that was, in absolute terms, the highest in the EU.
UK population grew by 419,900 to 63.7 million between between June 2011 and June 2012, according to ONS estimates.
There were 254,400 more births than deaths and 165,600 more people coming to the UK than leaving.
There were 517,800 migrants from overseas while 352,100 people left the country.
The UK remains the third-most populous EU member state, behind Germany and France.
France's population grew by 319,100 to 65,480,500 over the same period while Germany's went up by 166,200 to 80,399,300, says the ONS.
The mid-2012 populations of England, Scotland, Wales and Northern Ireland are now estimated to have been 53.5 million, 5.3 million, 3.1 million, and 1.8 million respectively.
London's population has surged by 104,000, with high birth and immigration rates.
Together London, south-east and east England accounted for 53% of growth across the UK in the year while Scotland, Wales and Northern Ireland jointly accounted for 8%.
More than 51,000 people moved out of London, largely to the South East and East of England, the ONS data shows.
London recorded net international migration of 69,000 - the highest of all regions. Northern Ireland had the lowest net migration growth of about 400, the ONS said.
The capital also recorded 86,000 more births than deaths in the past year, while Scotland notched up 4,200 more births than deaths.
Alp Mehmet, of campaign group Migration Watch, claimed that immigration was "the main driver of population growth in the UK".
Mr Mehmet highlighted earlier ONS data which showed babies born to foreign born mothers "now account for over a quarter of the total while births to UK born mothers are remaining static".
"These figures have a significant bearing on future needs like school places and housing as well as services," he said.
"This is why the government has to stay the course in its efforts to bring immigration under control."
But some economists argue that there are advantages in having more children.
Jonathan Portes, director of the National Institute of Economic and Social Research, said: "The medium to long-term benefits are substantial.
"The people who are being born now or the immigrants who are coming here now will help pay for our pensions and public services in the future."
A Home Office spokesman said: "Net migration is now at its lowest level for a decade showing we are continuing to bring immigration back under control.
"We will continue to work hard to bring net migration down from the hundreds of thousands to the tens of thousands by the end of this Parliament."
Royal College of Midwives chief executive Cathy Warwick said the high number of births was putting "considerable pressures on maternity services and we are struggling to provide high quality antenatal and postnatal care".
She said: "England remains around 5,000 midwives short of the number required to provide mothers and babies with the high-quality service they need and deserve.
"Maternity care is the earliest health intervention of all and getting care right for mothers and babies is a vital part of supporting families and building a foundation for good health in later life."
In January, Health Minister Dr Dan Poulter said there had been a "historical shortage" of midwives but he added: "The number of midwives is increasing faster than the birth rate."
There were 581,800 more children aged six and under in the UK in mid-2012 than in mid-2001.
But because of lower birth numbers around the turn of the millennium, the number of seven to 16-year-olds is 453,300 less than mid-2001.
At the other end of the population tree, the number of men aged 75 and over has increased by 26%, since mid-2001 compared with a 6% increase for women.
The ONS put this down to positive changes in male smoking habits and advances in health treatments for circulatory illnesses.
Male occupations over the same period have also become less physical and safer, it said.
Separately, the ONS has also released data showing that four million homes in the UK are still not connected to the internet.