The information requested falls within the responsibility of the UK Statistics Authority. I have asked the Authority to reply.
Dear Lord Hodgson,
As National Statistician and Chief Executive of the UK Statistics Authority, I am replying to your Parliamentary Question asking what assessment has been made of the difference between (1) the number of National Insurance numbers issued to non-UK nationals, and (2) total immigration to the UK in the last five years (HL12534).
The Office for National Statistics (ONS) publishes migration statistics and in 2016, looked at the differences between long term international migration (LTIM) figures and the allocation of national insurance numbers (NINos) to EU nationals and published papers about their findingsand the next steps.
The LTIM estimates produced by ONS are in line with the United Nations definition of a long-term migrant; intending to stay for at least 12 months. NINos are issued to people who come to the UK to work or look for work, regardless of the length of stay. NINos may therefore include short-term migrants (those entering the UK for less than 12 months) who will not be included in LTIM estimates. LTIM estimates will include people (such as students) who come to the UK for reasons other than work and don’t register for a NINo, so are not included in NINo data.
Further publications about improving the evidence and the migration statistics transformation programme include further information about how ONS is developing the evidence base on migration. Understanding the differences between data sources is an important part of our analysis within that programme and ONS will report further in due course.