<p>Any estimate of the exact size of the illegal population is extremely difficult and there would be considerable uncertainty around it. Similarly this applies to any estimate of the size of the illegal population committing crimes not least because not all crimes committed come to the attention of the authorities or lead to arrests; convictions; or removal action.</p><p>Exit checks were introduced in April 2015 and are, over time, providing more detailed insights into the behaviour of migrants and how they comply with the restrictions placed upon their length of stay in the UK. Instead of producing inaccurate numbers, the Government is focused on making it harder for people to live in the UK illegally.</p>