The UK's Office of National Statistics (ONS) has said the difference between two measures used to track immigration into the UK from EU countries can be explained by people coming to work for only a short time.
The difference in figures has been at the centre of a months-long political and media firestorm around accusations that official statistics underreported the "true" number of EU immigrants in the UK. Immigration has been at the heart of the campaign for Britain to leave the EU, so Thursday's release had the potential to swing votes.
The official measure, which is largely based on surveys of people arriving into the UK's airports and ports, shows that 257,000 people from the EU immigrated into the UK in the year leading up to September 2015.
However, during that time, 630,000 people from EU countries registered for national insurance numbers, which are required to work in the UK. Newspapers and political campaigners have pressed on the gap, with some (including The Sun newspaper) dubbing the gap a "migrant con".
The ONS's explanation for the gap between the figures is the result of a one-off analysis over the last several months of data from HM Revenue and Customs, the Department for Work and Pensions, and several other sources.
The statistical body concluded the principal reason the two figures were different was because a lot of people from the EU come to the UK to work short-term – for a period of a few months. Official migration statistics only include people who intend to stay in the UK for 12 months or longer.
The ONS used this chart to explain what was happening:
The orange line is the UK's official immigration figure for EU nationals. The blue line is the number of new national insurance registrations for the same years – clearly a far higher figure.
The green line is the result of one-off analysis by the ONS adding short-term international migration from EU nationals to the long-term figures. This figure includes people who come to the UK for work and study but stay for less than a year. The figures only include those who actually leave in the timespan they said they would – meaning they take a lot longer to collect than the long-term figures.
The dotted lines represent recent short-term migrants for whom there is not yet any data on whether or not they left, and so are forecasts rather than hard data.
The ONS also sought to explain the large recent spike in national insurance registrations from EU countries, saying it occurs when new countries gain access to the EU's labour market – the right to work in any EU country.
Controls on Bulgaria and Romania were lifted in 2014, leading to a spike in national insurance applications from those countries. The ONS noted that these often come from people who have lived in the UK for some time.
The ONS concluded that the official measure of immigration remains the most accurate UK statistic to measure the number of migrants in the country. The next release of immigration figures is due on 26 May, just four weeks before the EU referendum date.
Jonathan Portes, an academic who has been one of the leading voices questioning the official statistics, welcomed the ONS release but said he still believed the official figures under-estimated EU immigration.
"In my view, the evidence suggests that the migration statistics have in fact undercounted EU migration to the UK," he said. "In particular, the long-term international migration statistics show a gross inflow of EU citizens of 739,000 in the four years to June 2014, while the number registering for a NI number was 1,537,000."
Portes agreed with the ONS that short-term migration counted for much of this discrepancy, but said a group in HMRC's data marked as having a "longer term interaction" with UK employers suggested this may not account for the full divide.
Those HMRC figures, published in the ONS release, showed around one million EU
nationals had arrived, or registered for a NI number, in that four years had paid tax or received benefits over the period – a higher figure than the official statistics might suggest.
"Taken together, the DWP and HMRC data suggests to me that there was a degree
of undercounting of long-term migration from EU member states," he concluded. "I note ONS disagree with this view, and I respect their independent professional view. There are no clear "right answers" here."
Portes also added that the analysis used figures available up to 2014, which was before the spike in EU national insurance registrations in the wake of Bulgaria and Romania fully entering the EU's labour market without restrictions.
Priti Patel, the employment minister and Vote Leave supporter, said the figures showed the impact of migration was greater than official statistics suggest.
"These figures - which had to be dragged out of the government - show the scale and impact of immigration from the EU is even higher than previously admitted," she said. "It is out of control - and cannot be controlled as long as we stay in the EU. This puts huge strains on the NHS, housing, schools and other public services.
"Short term migration is highly significant, and arguably most damaging in terms of wages and work conditions. The only way we can take back control, and deliver on our manifesto commitment to reduce migration is to Vote Leave on 23 June."
The way short-term employment is defined in UK statistics can incorporate situations which could affect UK employment and wage conditions. This is because people coming to the UK for short-term work are classed as people who stay for less than 12 consecutive months, and this group makes up a large portion of those in the HMRC data.
This means, for example, that a builder coming to the UK for a six-month project, who then leaves for a few months and returns for another, would be a short-term migrant – but may arguably still take a job a British person could do.
The latest short-term immigration figures, which are published annually, are also expected to be released before the EU referendum.
James Ball is a special correspondent for BuzzFeed News and is based in London. PGP: here
Contact James Ball at James.Ball@buzzfeed.com.
Alberto Nardelli is Europe editor for BuzzFeed News and is based in London.
Contact Alberto Nardelli at firstname.lastname@example.org.
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