The country's population rose by nearly half a million last year, the highest annual growth rate for nearly 50 years as more babies were born than since the baby boom of the 1960s.
Figures released by the Office for National Statistics (ONS) show the UK's population stood at 62.3 million in the year leading up to mid-2010, an increase on the previous year's 61.8 million, giving it the highest annual growth rate since 1962.
Last year's annual growth rate was 0.8%, compared with a usual one of 0.6%, the ONS said.
Natural change (the difference between births and deaths) accounted for 52% of the UK population growth, with there being 134,000 more births than in the year leading up to mid-2002.
Statisticians said this is due to there being more women in the key childbearing ages of between 15 and 44 years old.
While there were 12.3 million women of key childbearing age in 2000/01, in 2009/10 there were 12.5 million women, the findings show.
Another factor is the number of women born in the 1960s and 70s who put off having children and are now having children at older ages than in the past.
Immigration has also contributed to the increase in annual births in the UK since 2002 due to the increasing population of non UK-born women who tend to have more children than their UK-born counterparts.
The lower number of deaths can be attributed to lower mortality rates due to medical advances, with circulatory diseases having seen the greatest fall in age-related mortality. In particular, the number of men aged over 85 has increased.
The population increase is in line with previous years over the last decade, and the third year in a row that natural change has been the cause of it rather than immigration.