• UK;
  • migration;
  • National Insurance Number (NINo) registrations;
  • Accession Countries;
  • New Member States (NMS);
  • Polish migrants


This paper addresses the challenge of measuring the extent of immigration to the UK following EU Accession in 2004, and argues that the most commonly used databases (UK Census, Labour Force Survey and Worker Registration Scheme) can be supplemented by the National Insurance Number (NINo) Allocations database, and demonstrates the utility of this data for future research by outlining the geography of immigration derived from NINo. The paper makes three important contributions through the thorough analysis of a data source currently underexploited in migration studies; first that the NINo, when used as a indicator of migration per se offers some interesting insights into migration in the UK, and secondly that as a tool for comprehensively measuring the registration of migrants working legally in the UK, it offers a means of constructing a internal geography of (legal) labour migration, as the paper demonstrates. Third, the analysis also identifies self-employment as a potentially important missing driver behind EU Accession Migration.