EU referendum: National Insurance registrations shows immigration to be higher than thought because of short-term migration, ONS says
The number of non-UK nationals registering for National Insurance (NI) numbers is higher than other official statistics due to short-term migration, long-awaited analysis has shown.
The Office for National Statistics (ONS) found a large number of people entered the UK for a short period of time (one to twelve months) over the past two years, which was not picked up by official immigration statistics.
Using a range of administrative and survey data, the ONS analysed the reasons why the number of NI numbers being registered has been higher than the number of people estimated as migrating to the UK, and why in recent periods the gap between the two figures has grown.
The ONS adds that short-term migration from the EU for work and study has grown, accounting for the difference between "long-term migrants" and NI registrations for EU nationals.
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There has been a push for information on the number of people from the EU who have paid income tax and national insurance, as well as received benefits. It is thought that details on NI numbers will reveal the current impact of EU migration, as opposed to
Official statistics count the number of foreigners into British air and sea ports, but that figure is different to those given national insurance numbers, and has been criticised for a lack of accuracy.
Since 2010 some 904,000 EU nationals moved to the UK, according to figures from the ONS. However, 2.25m national insurance numbers have been issued.
The latest ONS figures suggest that 257,000 EU migrants came to the UK between September 2014 and September 2015. However, in the same period 630,000 NI numbers were allocated to EU nationals.
The ONS said that the International Passenger Survey – which collects information about passengers entering and leaving the UK – is still the best source of information for measuring long-term international migration, while NI registrations aren't a good measure of long term trends as they don't indicate the "presence of an individual country, or how long they spend here".
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The release of data comes six weeks before the UK turns out to vote on the UK's membership of the European Union.
Leave campaigners have long been campaigning that the figures released by the ONS have underestimated the scale of immigration. They also say that the UK will not be able to control net migration inside the EU.
That appears to have been conceded by the government, as the Treasury report on the EU referendum assumes immigration will add three million people to the UK's population if the UK stays in the EU.
The data was initially requested by Jonathan Portes, a research fellow at the National Institute of Economic and Social Research. He previously wrote that official statistics were likely to have underestimated immigration, but in the absence of the data said he could not be sure.
He said of the release today: "It is clear that there has been a very large rise in short-term migration to the UK from the EU in recent years, and that this accounts for most of the divergence between National Insurance number registrations and the official immigration statistics, based on the International Passenger Survey"
"However, in my view, the evidence suggests that the migration statistics have in fact undercounted EU migration to the UK."