The migration statistics quarterly report published by the ONS has been reclassified as ‘experimental’ and will not be designated as national statistics.

The ONS has been changing the way it produces migration statistics to make use of more administrative data sources available following the passing of the Digital Economy Act in 2017. Outcomes from this analysis have been added to the quarterly migration statistics report, which relies mainly on findings from the International Passenger Survey.

While the latest findings support previously published estimates of headline migration, the research has indicated that EU migration may have been “somewhat higher” and non-EU migration “somewhat lower” than previously published, the ONS said in a statement.

Iain Bell, deputy national statistician, said: "These differences largely reflect uncertainty in intentions among specific groups. We have made adjustments based on the new data sources. These are giving us the best assessment yet of migration trends."

The ONS said it had understated emigration and overstated net migration for non-EU, primarily among students, which it attributed to people’s uncertainty when emigrating.

Immigration and net migration have also been understated from the EU8 countries – Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia, Slovenia – until 2016, the ONS said.

The International Passenger Survey collects information about passengers entering and leaving the UK. It has been running since 1961. Bell said: "ONS has been clear about its limitations. It is an intentions-based survey. There are indications that the link between intentions and behaviours are changing, particularly for some groups of EU and non-EU citizens."

The announcement was made yesterday ( 21st August), ahead of the latest migration figures, released today.

The ONS said its work to update the migration statistics is ongoing and that it expects to complete the programme by August 2020, when it plans to ask the UK Statistics Authority to reclassify the data as national statistics.

Ed Humpherson, director general for regulation, Office for Statistics Regulation, said: "Following the work undertaken to improve long-term migration estimates we conclude that the migration statistics quarterly report should no longer be designated national statistics, and support ONS’s proposal for the next MSQR to be classified as experimental statistics.

"It remains critical for decision makers, including politicians, businesses and the public to have robust and reliable migration estimates. I urge ONS and other government departments involved in the population and migration transformation programme to hasten progress and prioritise this development work to improve estimates, whether through data sharing, collaborative research work, or other sharing of expertise and resource."

Jonathan Portes, senior fellow, The UK in a Changing Europe and professor of economics and public policy at King’s College London, said: "My earlier research suggested that the ONS was underestimating recent migration of EU citizens to the UK, while overestimating non-EU migration. The ONS paper represents a welcome recognition of this issue. ONS should be commended for recognising the serious issues with the statistics and putting in place an ambitious programme of work to address them."

He added: “These developments also further illustrate the foolishness of the government’s net migration target – it was always a mistake to base policy on important issues like the visa system for skilled workers and students on arbitrary and inaccurate numbers rather than the needs of the UK economy.”