UK has 30,000 more European migrants than were recorded

NET migration from the EU into the UK has been officially underestimated by 16 per cent for more than a decade.

The measure, produced every three months by the Office for National Statistics (ONS), is the benchmark for policy making on migration. Health, school and local council officials also use the data to plan services.

Almost 30,000 more migrants had come from the EU8 countries, which include Poland, over a year than previously estimated – 207,000 rather than 178,000 as previously thought.

By contrast, the ONS overestimated net migration from outside the EU by around 13 per cent. The revised figure was 172,000, down from 197,000.

Quarterly immigration figures, to be published today, have been downgraded to “experimental statistics.”

The problems stem from the International Passenger Survey, based on asking 800,000 people a year about how long they plan to stay in the UK. EU migrants are highly mobile and their plans change.

Not all ports all the time are covered, and the sample works is just over 1 per cent of Heathrow’s annual traffic of 78 million people.

The ONS said a more robust system, which would draw on government data including the tax returns and benefits of migrants, health and education data, should be in place next year.

Iain Bell, deputy national statistician, said: “[The ONS has] been making use of all available data to get a richer and deeper understanding of migration as a priority since September 2017.”

However, there were clearly still “limitations” in the way the data was being assessed, he said.

Madeleine Sumption, director of the Migration Observatory at the University of Oxford, said: “We have been pointing out for a while that something wasn’t quite right in the net migration statistics, and that the comparison of EU versus non-eu net migration did not seem plausible.”

The disparity was significant, she added, because “for the past nine years the UK policy debate has been fixated on a single data source, which couldn’t bear the load” of interpretation being placed on it.

“Whether the question is how to meet the net migration target or what to do about international students, the truth is that the data were simply not robust enough to be picked apart in such detail,” Ms Sumption said.

“The quarterly drumbeat of migration statistics that has become a feature of the UK migration debate arguably over-dramatised small changes in figures that were always quite uncertain.”

Boris Johnson, the Prime Minister, and Priti Patel, the Home Secretary, are preparing to revamp Britain’s postbrexit immigration system by introducing points based on skills and the country’s economic needs.

Mr Johnson has distanced himself from Theresa May’s target of reducing immigration below 100,000, saying that he would “not be playing the numbers game”.