The peak level of net migration was higher than previously thought, at 944,000 in 2023, official data shows.
But vastly more Britons are emigrating leaving figures down over a longer period, the Office for National Statistics (ONS) figures said.
It included a new high for net emigration by Brits since Labour came to power.
Revisions to ONS data showed net migration – the difference between the number of migrants coming to live long-term in Britain minus the number of people emigrating – was 944,000 in the year to March 2023.
Previous figures had indicated the highest point was 906,000 in the year ending June 2023.
But in a dramatic development, hundreds of thousands more British citizens are turning their backs on this country and going to live abroad.
Over a four year period from 2021 to 2024, 344,000 more British nationals emigrated than previously thought, in net terms.
Passengers at the UK Border gates at Heathrow airport
Overall emigration by British nationals over the period was 650,000 higher and immigration by returning Brits was 306,000 higher, meaning net emigration was 344,000 above previous estimates.
The number of Britons emigrating has hit a new high under Labour.
Last year alone the number of Brits leaving the country was 257,000, far above than the 77,000 the ONS had previously estimated.
Before Labour came to power the previous highest number of emigrating Brits was in 2021 as international travel began to open up after the pandemic, with 283,000.
Net emigration – the number of Brits leaving minus those coming back – has also peaked since Labour came to power, data showed.
In the 12 months to September 2024 – just after the general election – a net 116,000 Britons left the country, far higher than previously thought.
The figure was 114,000 for the partly overlapping period of the 2024 calendar year.
By comparison, net British emigration was 69,000 in 2021.
All the revisions are due to the ONS improving its methods by using government data on the tax and benefits system to calculate its estimates.
These figures have replaced a survey of passengers at ports and airports, the International Passenger Survey (IPS), which the ONS said had been ‘stretched beyond its original purpose’.
‘Our new methods cause an upward revision in our British nationals emigration estimate over the past few years,’ an ONS spokesman said.
The changes means that net migration over the four year period is now put at 97,000 lower than earlier estimates had said.
Statisticians said there had been a ‘sharper fall’ in net migration since the peak was hit in 2023.
In May this year the ONS published estimates showing net migration was 431,000 in 2024 but today’s latest data revised that downwards to 345,000.
The data indicated that tough changes to the immigration system brought in by then Tory home secretary Sir James Cleverly in spring 2024 had a much larger effect than previously thought.
Tory home secretary Sir James Cleverly introduced measures to cut immigration levels in spring 2024 which had a more dramatic effect than previously thought, official new data shows
If the latest data had been available at the time of last year’s general election the Conservatives would have been able to claim much greater success in tackling the previous peak of net migration.
Mary Gregory, director of population statistics at the ONS, said: ‘Understanding the long-term international migration patterns of British nationals has been, and always will be, challenging due to the sheer number of British people crossing the border on a daily basis.
‘Based on these new data and methods, it is clear the IPS continued to underestimate British emigration since 2021, and it also underestimated immigration.’
