London’s population is on track to hit 10 million within the next decade driven by immigration rates running at about 100,000 a year and high childbirth figures among young immigrants, a new official report has found.

The influx means London is likely to hit megacity status by 2025, up from a population figure of 8.2 million in 2011, figures from the Office for National Statistics (ONS) show.

The study looked at eleven city regions across the UK and found that London was anomalous for a number of reasons.

First and foremost was London’s rate of growth – an astonishing 5.7 per cent between 2011 and 2015 – equivalent to an increase of more than half a million people in just four years. The figure is more than twice that seen on average across the other ten regions combined, while the rest of the UK, excluding the city regions, saw a population increase of only 2.5 per cent in the same period.

The increase is predominantly being driven by international migration; on average each year between 2011 and 2015 London saw 192,000 foreign migrants arrive and 95,000 leave, giving a net figure of 97,000 over each of the four years.

The headline figure, therefore, masks huge demographic shifts within the city, brought about in part through white flight. Census figures showed that some 620,000 native Britons have abandoned the city between 2001 and 2011, a trend which the ONS figures show continuing.

As a result, London posted three times as much internal immigration out of London (that is, Londoners moving to other parts of the country) as the next most abandoned city region, the West Midlands, which includes the city of Birmingham. The figures were 3.1 per cent net of the 2011 population for London, against just less than 1 per cent net for Birmingham.

Similarly, London was the only city in the study in which the net migration of children was negative, suggesting that families with young children in particular are abandoning the city, the report says likely in response to high house prices in the city.

The report notes: “On most measures shown in this report, Greater London stands out. It is by far the UK’s largest city region but is also the fastest growing. Its comparatively young population age structure means it has a higher birth rate and a lower death rate than other areas.

“In addition its attraction as the UK capital, a major employment centre and international hub lead to much higher growth from international migration than any other area.

“For internal migration, however, Greater London has a high net outflow. Uniquely among the city regions it has a high net internal inflow of people aged 22 to 29, reflecting its attraction for graduates in particular. But in other age groups larger numbers of people move out, with potential reasons including the high cost of property for people forming a family, plus lifestyle choices.”

London is already seeing huge differences on the ground as a result of the population shift. In a documentary filmed earlier this year locals in the borough of Newham, once the heart of London’s cockney culture, described the area as “Baghdad” thanks to decades of immigration from India and Pakistan. Meanwhile locals have departed, mainly for Kent.

Ethnic minorities make up 76 per cent of the borough’s population, making it the most multicultural place in Britain, prompting one local to comment “It’s hard to find somebody who speaks English in Newham.”