Driven by data; ridden with liberty.
After the latest round of migration statistics from the Office for National Statistics (ONS), The Sun newspaper suggested that these figures were a ‘CON’ . UKIP MEP Steven Woolfe, the party’s spokesperson for migration, said:
It seems the public are being conned.
This refers to the discrepancy between the number of incoming migrants from the EU, according to the ONS, and the number of new National Insurance Number (NINo) registrations, according to the Department for Work & Pensions (DWP). This discrepancy has been investigated by Jonathan Portes, of the National Institute of Economic and Social Research .
The February release of the migration statistics found that 617,000 people came into the country on a long-term basis, and 294,000 people had emigrated . This meant that long-term net migration was 323,000, up by 31,000 from the year-end September 2014). From other countries in the European Union, the immigration figure was 257,000.
Across 2015, there were 630,000 new registrations of National Insurance numbers for EU nationals . This increase in NINo registrations to EU nationals is caused by a surge in registrations to citizens from Romania and Bulgaria.
The estimate for long-term migration comes from the International Passenger Survey, conducted by the ONS. Incoming passengers at airports, sea and train routes across the country are surveyed, and asked how long they intend to stay. Only those people who intend to move for more than a year are considered to be immigrants or emigrants in the survey. This is the international standard definition for migration.
NINo registrations are a 100% sample, which is a count of all such registrations. According to the February report:
The NINo statistics show the number of people registering for a NINo in order to work or to claim benefits / tax credits and are one of a number of supplementary measures produced by Government of in-migration to the UK.
They are a measure of in-flow to the UK, primarily for employment, including both short-term and long-term migrants and include foreign nationals who have already been in the country but not previously required a NINo as well as migrants who may have subsequently returned abroad.
There are definitional and operational differences between the two sets of figures. The ONS figures do not measure trips to the UK for less than a year, such a summer job. The NINo registration is allocated against the time at which it was requested, and not when the person arrived: they are not a direct measure of immigration.
The ONS figures is an estimate for all types of inward migration, but the NINo counts are for people of working age only. The ONS figures are based upon a passenger survey, and so could be providing an under-weighting for certain airports or routes into the country. The NINo registrations are an actual count, potentially subject to fraudulent activities.
It is not possible to determine the magnitude of these effects, or the scale of the error, if non-zero, in the official migration statistics provided by the Office for National Statistics.
If the DWP provides counts for activity and persistence of their National Insurance numbers, then that data should be illuminating.
 The Sun, 2016. The Great Migrant CON: MPs accused of a ‘cover-up’ as we reveal that 630,000 registered to work in 2015. Available from: http://www.thesun.co.uk/sol/homepage/news/politics/6958099/Ministers-accused-of-a-cover-up-over-migrant-figures.html [Accessed: 17th March 2016]
 Portes, J., 2015. Recent EU migration to the UK: can we trust government numbers? NIESR. Available from: http://www.niesr.ac.uk/blog/recent-eu-migration-uk-can-we-trust-government-numbers#.VusIvfmLTIW [Accessed: 17th March 2016]
 ONS, 2016. Migration Statistics Quarterly Report: February 2016. Available from: http://www.ons.gov.uk/peoplepopulationandcommunity/populationandmigration/internationalmigration/bulletins/migrationstatisticsquarterlyreport/february2016 [Accessed: 17th March 2016]
 DWP, 2016. National Insurance Number Allocations to Adult Overseas Nationals: Quarterly Report-Registrations to December 2015. Available from: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/502613/nino-registrations-adult-overseas-nationals-feb-2016.pdf [Accessed: 17th March 2016]