UK Edition
Around 50,000 people left Britain in the three months after Covid struck last year as work dried up and the economy collapsed.
The fall, for the three months to June 2020, is the first net emigration recorded by the Office for National Statistics (ONS) since it began collecting quarterly data and suggests that migrant workers returned to their home countries in the wake of lockdown.
It only covers the initial impact of Covid-19 but is a smaller drop than initially feared, after previous estimates suggested that anywhere between 200,000 and 1.3m people could have left Britain.
Separate figures suggest the ONS has significantly underestimated the number of migrants coming to Britain from the European Union since 2012.
Although lower than anticipated, the 2020 outflow of workers still represents a rare and sudden reversal in the usual influx of workers, students and travellers. Over the 12 months to June net migration was around 282,000, the ONS said.
Quarterly estimates date back to 2010 and have never shown a net outflow of migrants. On annual data, the last year in which more people left the UK than arrived was 1993.
Combined with deaths caused by Covid and slowing births, the shift to emigration pushed the UK's population growth down to the slowest pace since 2003 in a fall which could hold back future economic growth.
In the middle of 2020 the population stood at 67.1m, a rise of 0.5pc on the year.
That compared with a recent peak of just over 0.8pc in 2016, and a trend over the past 15 years for growth of about 0.7pc.
In the 1990s, growth was much slower at about 0.3pc per year.
Depending on patterns of migration in the second half of 2020, the UK is likely to have a significantly smaller population than previously anticipated as a result of Covid.
If migration resumed and a net 100,000 people moved to Britain, the ONS estimates the population ended 2020 at 67.2m.
However, if emigration continued at 50,000 per quarter, that would bring the population down to 67m. It means the population will fall short of pre-Covid expectations of 67.36m by between 150,000 and 350,000 people.
Evidence from countries including Italy and France indicates the pandemic may also have triggered a baby bust after would-be parents were put off from having childen due to economic turmoil. This could have an even larger effect on the population as there are usually more than 700,000 births annually, although official data has yet to be released.
Economists have suggested Britain's rapid vaccine rollout could allow the economy to reopen sooner than many places on the Continent, encouraging renewed migration as workers seek opportunities again later in 2021.
Meanwhile historic migration levels may have been underestimated, according to new data based on national insurance figures.
Tax and benefits numbers indicate there were around 123,000 more arrivals in the year to March 2012 than previously estimated. In the 12 months to March 2016, there were 215,000 more.
This means EU net migration peaked at close to 300,000 in 2015 and 2016 - rather than just above 200,000 as previously thought. It then fell to around 120,000 in 2019-20, rather than just above 50,000 as estimated before.
Meanwhile net migration from outside the EU was around 50,000 less each year than previously thought.
Overall it suggests net migration has been understated by an average of almost 43,000 per year since 2012.