The estimated number of illegal (unauthorised) immigrants currently living in the UK ranges broadly, with recent estimates in 2025 suggesting figures between around 600,000 to over 1 million. Specifically, Oxford and London- based studies from recent years estimate between approximately 594,000 and 745,000 illegal immigrants including children, with some estimates reaching as high as 1.2 million, though the latter is considered outdated or unreliable. The Pew Research Center's earlier higher range (800,000 to 1.2 million) was revised downward in 2025 to about 700,000 to 900,000. Additionally, arrivals by small boats crossing the English Channel in 2025 have already exceeded 25,000, adding pressure to the total unauthorised population. Overall, estimates remain uncertain due to the hidden nature of this population, but the consensus suggests hundreds of thousands to just over a million illegal immigrants reside in the UK at this time.
