How many people are in the UK illegally?
It is the most-asked question about this subject, and it has an honest answer that is not a number.
Nobody publishes it — including the Home Office, which says so in writing. Every figure that gets quoted as an answer is either counting something else, or is an estimate produced outside government on its own assumptions.
The department says so itself
“It is not possible to know the exact number of people currently resident in the UK without permission, nor the total number of people who enter the UK irregularly, and so we do not seek to make any official estimates of the illegal population.”
That is not an evasion. It follows from what the statistics are: a count of encounters. A person can enter undetected, or enter lawfully and overstay, and in neither case does an event get recorded that a statistician could count. There is no register of people present without permission for the same reason there is no register of undetected anything.
What is actually counted
These are the real figures, each linked to its own page and source. Read what each one counts before reading the number: several are flows (events over a period) and several are snapshots (a state on one day), and the two cannot be combined.
Why these do not add up to an answer
Most of them are not about people here illegally. Someone who has claimed asylum and is awaiting a decision is lawfully present while it is considered. Someone in receipt of asylum support is, by definition, in the system rather than outside it. Counting them as “illegal immigrants” is not a stricter reading of the data, it is a different claim about a different group.
Flows are not stocks. Arrivals, claims and returns count events over a period. Adding several years of arrivals produces the number of arrival events, not the number of people still here: people are granted status, are removed, leave voluntarily, or die, and every one of those exits is invisible in an arrivals series.
The same person can appear more than once. Detection counts are counts of encounters. So are the detention figures — a person detained twice appears twice, which is why the detention-length table says occurrences rather than people.
Whole categories are missing by design. The user guide lists who is not in these statistics: people who arrive undetected through any method of entry, people who arrive hidden in a vehicle on a ferry or on larger vessels, people who enter through the Common Travel Area, and — the largest unknown of all — people who arrive entirely lawfully and overstay their visa.
The publisher says not to try. On comparing its own datasets, the guide is explicit:
“it is not advisable to directly compare different datasets, or possible to infer the total number of people attempting to enter irregularly through each method of entry. Therefore, the statistics should not be used to infer relative attempts through each method of entry.”
Estimates of the irregular population do exist — produced by academics, think tanks and campaign groups, on their own assumptions, and differing from each other by orders of magnitude. This site publishes official figures, so it carries none of them, and it is not in a position to tell you which is closest to right. What it can tell you is what the official statistics are and what their publisher says they cannot support, which is on this page.
The Office for National Statistics published a note on measuring illegal migration in June 2019, referenced in the Home Office guide above; it is worth reading precisely because it explains the difficulty rather than resolving it.
What would have to exist for the question to be answerable
A count of people present without permission requires knowing who is here and who has left — an entry and exit record matched per person, across every route in and out, sustained over years, with status changes tracked as claims are granted and refused. Nothing in the published statistics is that. Until it is, the honest position is the one the department itself takes, and anyone quoting a precise total is quoting an estimate someone constructed, whether or not they say so.
Data as of
Cite this page
How many people are in the UK illegally?. Migration Watchdog, data as of 2026-08-21. https://migrationwatchdog.com/how-many Underlying figures: UK official statistics, re-published under OGL v3.0 — every figure links to its source on the page.
Sources for this page
- Home Office irregular migration to the UK statistics: user guide — Home Office · updated 2024-11-28 · retrieved 2026-08-21
- Illegal entry routes to the UK summary tables, year ending March 2026 (Home Office) — Home Office · calendar years, published in the year ending March 2026 release · retrieved 2026-08-17
- Asylum summary tables, year ending March 2026 (Home Office, Immigration system statistics) — Home Office · as at 31 March 2026 · retrieved 2026-08-21
- Returns summary tables, year ending March 2026 (Home Office, Immigration system statistics) — Home Office · year ending March 2026 · retrieved 2026-08-17
Contains public sector information licensed under the Open Government Licence v3.0.