Sir,
It is misleading to suggest that the ONS estimates of immigration in 2015 were an "underestimate" ('Why do we lack the political will to deal with migration?', Daily Express, 4 August) because a larger number of National Insurance numbers (NINos) were issued over the same period. NINo registrations data only measure those registering for work and are not a good measure of long-term international migration. They also contain short-term migrants who leave the country within 12 months. A recent ONS analysis indicated that our estimates were robust and reliable, and remain the most appropriate for measuring long-term immigration.
Yours faithfully
Jay Lindop
Head of Population Statistics Division
Office for National Statistics