ONS underestimated EU net migration from mid-2000s to 2016
Levels of migration from the EU to the UK from the mid-2000s to the year 2016 were underestimated by the Office for National Statistics.
The ONS has admitted that the numerical error affected the overall number of migrants thought to have come from eight nations which joined the bloc in 2004.
It is also thought to have impacted the estimated number of migrants to have come from countries outside the EU.
The immigration figures from the time have since been downgraded to “experimental”.
An ONS statement said: ”Whilst we go through this transformation journey, we have sought to re-classify our migration statistics as 'experimental statistics' in line with Office for Statistics regulation guidance”.
Recent analysis of ONS figures showed that in 2015-16, EU net migration was 16 per cent higher than first thought, equating to 29,000 more people entering the UK.
This increased the estimated EU migration number from 178,000 to 207,000 for the year ending March 2016, while net migration from outside of the EU was 13 per cent lower than thought.
The ONS also said in February this year that net migration from non-EU countries to the UK had reached a 15-year high.
The ONS’ system for measuring migration, the International Passenger Survey, will now come under more scrutiny.
The system, in place since 1961 for the purpose of helping government better understand the economic impact of travel and tourism, surveys 800,000 people a year, using data from 250,000 of those people to estimate the number of people arriving to live in the UK against those leaving the UK for at least a year.
The survey doesn’t cover all ports at all times and the size of the samples of data used to conduct estimates has cast doubt on its efficiency.
The new figures also reveal that David Cameron’s Conservative government fell shorter than previously thought of their target to reduce net migration to under 100,000 people a year, a target which came under much scrutiny at the time.
Indeed, during the 2017 snap election, specific targets for immigration were left out of the Conservative manifesto with then home secretary Sajid Javid promising that they would be reduced to “sustainable levels”.
Madeleine Sumption, director of the Migration Observatory at the University of Oxford, believed that “something wasn’t quite right” with net migration figures for some time.
Sumption said: "This matters because for the past nine years the UK policy debate has been fixated on a single data source, which couldn't bear the load that it was forced to carry.
"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.”
The ONS was defensive in its response, saying that one data source is more than able to "fully reflect the complexity of migration”, but “a much clearer picture” could be gathered from examining other sources of information.