The number of people living in the UK's most populous city regions surged by almost 900,000 in four years.
Greater London saw the sharpest jump in population, with an increase of 5.7%, or nearly 500,000 residents, from 8.2 million in mid-2011 to just under 8.7 million in mid-2015.
Statisticians examined population data relating to the capital and the next 10 most populous city areas.
All saw an increase in inhabitants, with the total population across the 11 regions rising by 3.4%, or 885,000 in four years, to reach almost 27.2 million in 2015.
The report from the Office for National Statistics said: "All city regions have grown in population since 2011 and are projected to continue to grow. Greater London has had, and is projected to have, the most rapid growth."
Data showed that on average, the areas other than Greater London have grown slightly more slowly than the rest of the UK.
Bristol saw the second highest growth with 4.5%, while Glasgow had the smallest rise at 1%. As a whole, the city regions excluding London increased by 2.3% on average.
Change in the population size is caused by a combination of births, deaths, migration from within the UK and international migration, the study said.
Net long-term international migration - the difference between the numbers arriving and leaving - was estimated at an average of 153,000 a year between 2011 and 2015 across the city regions. Greater London accounted for more than half of the figure, with 97,000 a year.
The report said all areas saw a population gain from international migration - but the proportional rise in Greater London was more than twice that in any other city region.
"London's attraction to immigrants no doubt reflects its status as a major employment centre and international hub," the study said.
"With its high ethnic minority population it may prove especially attractive to people wishing to join family or others from that cultural background.
"In addition, for people heading to the UK, London is somewhere they are more likely to have some pre-existing awareness of than other parts of the country - perhaps because of previous visits, but also simply because it has a higher profile as the UK capital."
Patterns of internal and international migration were very different, according to the research.
While some city regions have had population increase from internal migration, on average there has been a net outflow to the rest of the UK.
On the other hand all areas have seen growth from international migration, with a concentration of immigrants in the 22 to 29-year-old age group, the report added.
All city regions had more births than deaths, although in some cases the difference was small.
The areas covered in the article are: Greater London, Bristol, West Midlands, Greater Manchester, Edinburgh, West Yorkshire, Sheffield, Cardiff, North East, Liverpool and Glasgow. Together they account for more than two fifths of the total UK population of 65 million.
The report concluded that the findings suggest that although they may differ in physical characteristics from other areas of the country, city regions are not inherently distinctive in terms of population dynamics.
"Instead they vary considerably, but with Greater London markedly different from the rest," it added.