The country's population rose by 394,000 last year, according to statistics out today.
The country's population stood at 61.8 million in 2008/09, up 0.6% on the previous year, figures released today by the Office for National Statistics found.
The increase is in line with previous years over the last decade but it is only the second time since 2000 that migration has not been the main cause of a population rise.
In 2008/09 there were 123,000 more births than seven years earlier.
According to the data, married women in their twenties and early thirties are more likely to give birth than their peers living out of wedlock.
But women aged 35 and above, who choose not to marry, showed higher fertility levels than those their same age who were married.
Net migration, the difference between immigration and emigration, fell last year. The country's population rose by 176,000 as a result of migration, down on the previous year by 15,000. But it is still 23% higher than in 2002 when net migration stood at 143,000.
The Government said today it was keen to slash the number of migrants coming to the UK, which stood at 562,000 last year, down slightly on the previous year.
Immigration Minister Damian Green said: "We believe that immigration has been far too high in recent years, which is why the new Government will reduce net migration back down to the levels of the 1990s - to tens of thousands rather than hundreds of thousands.
"Over the coming weeks and months the public will see us tackle this issue by introducing a wide range of new measures to ensure that immigration is properly controlled, including a limit on work permits, actions on marriage and an effective system of regulating the students who come here."Reuse content