Guidance

Home Office irregular migration to the UK statistics: user guide

Updated 28 November 2024

1. Introduction

This user guide relates to the ‘How many people come to the UK irregularly?’ chapter within the Home Office’s ‘Immigration system statistics quarterly release’. It is designed to be a useful reference guide, with explanatory notes on the issues and classifications which are important to the production and presentation of this chapter. The chapter itself provides information on irregular migration to the UK, including small boats.

2. Statistics covered

2.1 Detections of arrivals to the UK by irregular methods of entry

The number of people detected arriving to the UK irregularly by nationality, sex and age group, by the following selected methods of entry:

• small boat arrivals
• inadequately documented air arrivals
• recorded detections in the UK
• recorded detections at UK ports

2.2 Asylum claims from small boat arrivals

The number of asylum claims lodged by small boat arrivals, and initial decisions on these asylum claims.

2.3 Modern slavery referrals for small boat arrivals

The number of modern slavery (National Referral Mechanism (NRM)) referrals from small boat arrivals and outcomes of these referrals.

2.4 Returns of small boat arrivals

The number of enforced and voluntary returns from the UK of small boat arrivals.

2.5 Data tables

A complete list of published data on irregular migration to the UK can be found in the ‘Irregular migration detailed datasets and summary tables’.

3. Data source

3.1 Small boat arrivals

Data on small boat arrivals comes from 2 sources. The first, used for the total number of small boat arrivals, is a manually collated record of arrivals, collated by Border Force officers.

The second, used for the more detailed breakdowns (for example, small boat arrivals by nationality), is a more detailed dataset where further information is recorded as each arrival is processed. This includes information on asylum claims and modern slavery referrals. This dataset is sourced from Home Office administrative data systems, specifically the Case Information Database (CID) and Atlas, and from the Home Office database Pronto. As cases make progress, caseworkers enter information onto case working systems for operational purposes.

Data for some periods, particularly more recent periods, may have cases where a full breakdown is not yet available. These cases are reported as ‘Not currently recorded’ in the irregular migration data tables.

3.2 Inadequately documented air arrivals

Data on inadequately documented air arrivals comes from Home Office administrative data systems, specifically Atlas, where information on people without adequate documents or with fraudulent documents is recorded by Border Force Officers.

3.3 Recorded detections in the UK and at UK ports

Data on recorded detections in the UK and at UK ports comes from the Home Office database Pronto, where detections are recorded by Immigration Compliance and Enforcement teams and Border Force Officers.

4. Background on the statistics

The data counts the number of detections rather than individuals. One individual may be detected entering the UK irregularly more than once in a given period and, if that were the case, would be counted more than once in the statistics. On the other hand, there may be people who have evaded detection altogether and therefore will not be counted in the datasets.

4.1 Small boat arrivals

A ‘small boat’ is one of a number of vessels used by individuals who cross the English Channel, with the aim of gaining entry to the UK without a visa or permission to enter - either directly by landing in the UK or having been intercepted at sea by the authorities and brought ashore. The most common small vessels detected making these types of crossings are rigid-hulled inflatable boats (RHIBs), dinghies and kayaks.

The statistics in this chapter include individuals who:

• are detected on arrival to the UK
• are detected in the Channel by UK authorities and subsequently brought to the UK

4.2 Other entry methods

Data on other modes of irregular entry is derived from Home Office Management Information. Admin data is not designed for statistical purposes and should therefore be interpreted with caution. For more information, see section 5. Data quality.

Data on inadequately documented air arrivals relates to individuals who intentionally attempt to arrive in the UK through air routes either without adequate documentation or using fraudulent documentation. It does not include passengers who have genuinely made a mistake, lost their documents, or have arrived inadequately documented for reasons outside of their control. It does not include those who were prevented from boarding at their port of embarkation.

Data on recorded detections in the UK relates to detections of individuals outside of the controlled environment of a port, who when encountered are believed by authorities to have evaded border controls to enter the UK irregularly, up to 72 hours before being detected. It includes detections at the ports serviced by the juxtaposed controls (Dover, Cheriton/Longport and St Pancras), as the border control checks happen in France and Belgium before people begin their journey to the UK.

Data on recorded detections at UK ports includes individuals attempting to enter the UK irregularly at ports. It includes, for example, those detected at ports in lorries, and shipping containers. It does not include detections at ports that are serviced by the juxtaposed controls (Dover, Cheriton/Longport and St Pancras) or those prevented from leaving their port of embarkation en route to the UK, such as those detected at the juxtaposed controls in France and Belgium.

4.3 Statistics not included in this chapter

These statistics do not include individuals who:

• arrive on larger vessels, such as go-fast craft, yachts (except those arriving in the area of operations of small boats), motor cruisers, tugs and fishing vessels – although these are rarely used by irregular migrants at present
• arrive in the UK irregularly on larger vessels not referenced above, including where hidden in a vehicle on a ferry
• arrive in the UK undetected (through any method of entry), or where there have been reports of people making the Channel crossing, but no actual encounters
• enter through the common travel area
• overstay their visa

Prevented attempts to enter the UK are also not counted in this chapter, for example people who:

• are prevented from departing France on a small boat, or those intercepted by French authorities and returned to France
• seek to enter the UK without valid permission but are prevented from reaching the UK border (for example, at the juxtaposed controls in France and Belgium, or further afield, if prevented from travelling - for more information on juxtaposed controls, see ‘The UK’s juxtaposed border controls’ fact sheet)

For more information, see section 6. Limitations.

4.4 Asylum claims from small boat arrivals

The statistics on asylum claims in the ‘How many people come to the UK irregularly?’ chapter of the ‘Immigration system statistics quarterly release’ are specifically about small boat arrivals applying for asylum and initial decision outcomes on their claims. Data on all asylum claims, including those from non-small boat arrivals, is published in the ‘Immigration system statistics quarterly release’ in the asylum and resettlement datasets.

Dates are mostly based on date of arrival not asylum claim or outcome date, except for summary tables Irr_02f and Irr_02g which are based on date of outcome. Multiple people may be associated with the same asylum claim (that is dependants on a main applicant’s claim).

An asylum applicant (also referred to as ‘asylum seeker’) is someone who makes a claim to be recognised as a refugee under the Refugee Convention. The core principle of the Convention is that a refugee should not be returned to a country where they face serious threats to their life or freedom. The Convention outlines the definition of the term ‘refugee’, the rights of refugees and the kind of legal protection, other assistance and social rights they should receive from the countries who have signed the document. An individual seeking international protection is expected to claim asylum in the first safe country they reach, or by approaching the United Nations High Commissioner for Refugees (UNHCR). Asylum applicants will receive a decision on their claim, which may be a grant of refugee status (or ‘asylum’), humanitarian protection, or another form of permission to stay, or a refusal.

Initial decisions on asylum claims relate to the first decision given by the Home Office. An initial decision may subsequently be overturned following an appeal or reconsideration.

For more background information on asylum, see the ‘Asylum’ section of the ‘User guide to Home Office immigration system statistics’.

4.5 Modern slavery referrals for small boat arrivals

The statistics on NRM referrals in the ‘How many people come to the UK irregularly?’ chapter of the ‘Immigration system statistics quarterly release’ are specifically about small boat arrivals with modern slavery referrals. For further information and statistics on all NRM referrals, see the National Referral Mechanism statistics collection.

Modern slavery includes any form of human trafficking, slavery, servitude or forced labour. Potential victims of modern slavery in the UK are referred to the National Referral Mechanism (NRM).

NRM referrals can be made at any stage after arrival into the UK. NRM referrals may be triggered by, or occur after, other immigration events (such as, detention in preparation for return).

Dates are based on date of arrival not the date of NRM referral or decision and count the number of referrals. NRM referrals can be made at any stage after arrival into the UK. The number of small boat arrivals in each year with NRM referrals is likely to increase over time as people have more time to be identified and referred into the NRM.

When referred to the NRM, the Home Office makes a ‘reasonable grounds’ decision on whether an individual could be a victim of modern slavery.

Reasonable grounds decisions are those taken by the competent authorities to determine if there are reasonable grounds to believe, based on objective factors but falling short of conclusive proof, that a person is a victim of modern slavery (human trafficking or slavery, servitude, or forced or compulsory labour).

Adults given a positive reasonable grounds decision can have access to support if they need it. In England and Wales this support includes accommodation, financial support and other material assistance, legal aid and medical treatment while pending a ‘conclusive grounds’ decision on their case. Local authorities support children.

Conclusive grounds decisions are those taken following a positive reasonable grounds decision by the competent authorities as to whether, on the balance of probabilities, there are sufficient grounds to decide that the individual being considered is a victim of modern slavery.

Adults in NRM support in England and Wales who receive a positive conclusive grounds decision receive a minimum of 45 days of ‘move-on’ support, after which they can continue to receive support on a needs-basis until they exit through the Recovery Needs Assessment process. Those with a negative decision receive 9 days of ‘move on’ support as the individual exits NRM support.

The Devolved Administrations in Scotland and Northern Ireland provide support to victims. In Northern Ireland individuals will receive support for at least 45 days while their case is considered. In Scotland, individuals will receive support for 90 days or until a conclusive grounds decision is made, whichever comes sooner. However, in some cases support may be offered beyond the 90 days if a Conclusive Grounds decision has not yet been made.

The number of small boat arrivals in each year with NRM referrals may increase, as time will allow more people to identify as potential victims and be referred into the NRM.

The time periods between National Referral Mechanism statistics collection and these statistics do not align. These statistics relate to the date of arrival into the UK whereas the NRM statistics are based on date of referral into the NRM or date of decision.

4.6 Returns of small boat arrivals

The Home Office seeks to return people who do not have a legal right to stay in the UK. For returns of small boat arrivals, this includes:

• enforced returns (people subject to administrative removal or deportation action which is carried out by the Home Office)
• voluntary returns (people who were liable to removal action or subject to immigration control but have left of their own accord, sometimes with support from the Home Office)

Dates are based on date of return. The arrival was not necessarily in the same period.

Data only includes the earliest enforced or voluntary return after a small boat arrival. Subsequent returns following an alternative arrival method are not included, as they are not directly related to the small boat arrival.

This data relies on matching small boat arrival data with returns data. Therefore, there may be a small number of arrivals who have been returned but are not included in these figures, as their small boat arrival and returns records could not be matched properly, for example, small boat arrivals for whom more detailed information is not currently recorded.

Data on voluntary returns is subject to upward revision, so comparisons over time should be made with caution. In some cases, individuals who have been told to leave the UK will not notify the Home Office of their departure from the UK. In such cases, it can take some time for the Home Office to become aware of such a departure and update the system. As a result, data for more recent periods will initially undercount the total number of returns.

The Home Offices publishes information about numbers of all enforced, voluntary, and port returns in the returns datasets in the ‘Immigration system statistics quarterly release’.

For more background information on returns, see the ‘Returns’ section of the ‘User guide to Home Office immigration system statistics’.

4.7 Time periods

Published statistics time periods are based on calendar year and quarters. These are listed below.

All time periods (unless otherwise stated) in the chapter are currently based on the date of arrival to the UK, whether the data is reporting on arrivals, asylum or NRM processes.

Quarter 1 (Q1) relates to January, February, and March.

Quarter 2 (Q2) relates to April, May, and June.

Quarter 3 (Q3) relates to July, August, and September.

Quarter 4 (Q4) relates to October, November, and December.

5. Data quality

These datasets only cover known detections of irregular arrivals and do not cover those who have evaded detection. Additionally, there will be instances where a detection may not be recorded on the system, for example due to the detection being more than 72 hours after the arrival or due to limitations in admin datasets. The extent of these will vary between datasets and as such, 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. Small boat arrivals are the most visible of the irregular methods of entry, so the most likely to be detected.

To ensure the data is produced to a high standard, several sense checks and data quality checks are undertaken on the data each quarter, for example, to identify any missing data, along with reconciliation with other analytical and operational teams. Any inconsistencies are flagged with operational teams who undertake both regular and ad hoc data cleansing exercises to ensure information recorded on case working systems is as accurate as possible.

Our statistical practice is regulated by the Office for Statistics Regulation (OSR), which sets the standards of trustworthiness, quality and value in the Code of Practice for Statistics that all producers of official statistics should adhere to. You are welcome to contact us directly by emailing MigrationStatsEnquiries@homeoffice.gov.uk with any comments about how we meet these standards. Alternatively, you can contact OSR by emailing regulation@statistics.gov.uk or through the OSR website.

6. Limitations

The statistics presented here relate to the number of people detected on, or shortly after, arrival to the UK through various irregular methods of entry. They do not include all those who enter the UK through irregular methods, nor the number of irregular migrants currently present in the UK. 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. In June 2019, the Office for National Statistics (ONS) published a note on ‘measuring illegal migration’.

A small boat is only one of a number of irregular methods by which a person may reach the UK border and seek entry without permission. This chapter provides additional statistics on other irregular modes of entry but not all irregular entries will be recorded. Some people may enter the UK on regular routes and their status subsequently becomes ‘irregular’ (for example, if they overstay their visa). Others may enter through an irregular method and remain undetected or will be detected sometime after their arrival. Other people may enter irregularly but obtain ‘regular’ status (for example, following an asylum claim).

Figures on detections may be affected by the levels of operational activity at the border and overseas, so should not be used to infer levels of irregular migration. Changes in detection could be a result of changes in operational activity (for example, changes in the number of patrols or vehicle checks) as well as changes in the number of people attempting to enter the UK irregularly and recording practices.

7. Revisions to data

Data published in the ‘How many people come to the UK irregularly?’ chapter is taken from live operational databases, and as such is subject to revision, in line with the published Home Office revisions and corrections policy.

Reasons for scheduled revisions include:

• late reporting of cases – some cases may be entered onto the system after the time that the data extracts are initially taken
• changes to cases – as cases develop, some of the details of the case may be updated
• data cleansing – data cleansing exercises may lead to changes to the data on the source system

Data is revised on an annual basis in the August edition of the Immigration system statistics. For example, data for 2023 was revised in the August 2024 release.

Until these revisions have occurred, data should be considered provisional.

There may be occasions where unscheduled revisions are required. Any revisions or corrections are dealt with according to the published Home Office revisions and corrections policy.

Further details on the Home Office revisions policy can be found in the Statement of compliance with the code of practice for statistics.

Table 1: Revisions to the annual 2023 figures first published in February 2024

Method of entry	Published Feb 2024	Revisions published Aug 2024	Percentage change
Small boat arrivals	29,437	29,437	0.0%
Inadequately documented air arrivals	3,822	3,854	+0.8%
Recorded detections in the UK	3,117	3,081	-1.2%
Recorded detections at UK ports	328	327	-0.3%

8. Operational and policy context

On 24 March 2021, the Home Office published the New Plan for Immigration which set out the then government’s plans for the asylum and illegal migration system, set out in the ‘New Plan for Immigration: legal migration and border control’ policy paper.

On 14 April 2022, the then government signed a Migration and economic development partnership (MEDP) between the UK and Rwanda which established a legal framework under which anyone entering the UK illegally after 1 January 2022 could be considered for relocation to Rwanda to have their asylum claim decided. On the 22 July 2024, the new Labour Government announced that they were ending this partnership.

On 28 April 2022, the Nationalities and Borders Act introduced further changes aimed at streamlining asylum claims, improving the Home Office’s ability to return people with no right to remain, raising the threshold for modern slavery claims and introducing new criminal offences for illegal entry.

On 13 December 2022, an agreement between the UK and Albania was signed to disrupt irregular migration and criminal networks.

On 20 July 2023, the Illegal Migration Act was passed and introduced a law under which anyone arriving in the UK illegally will not be able to stay here and will instead be detained and then promptly removed, either to their home country or a safe third country.

On 10 March 2023, an agreement between the UK and France was announced to increase cooperation around preventing Channel crossings.

On 18 April 2024 an agreement between the UK and Vietnam was signed to increase cooperation on dealing with irregular migration.

On 7 July 2024, the Home Secretary launched the new Border Security Command, to boost Britain’s border security and deal with organised immigration crime.

On 22 July 2024, the Home Secretary made a statement to the House of Commons on her immediate plans relating to the asylum system which included action to speed up asylum processing and help clear the backlog. The Home Secretary set out a change to the law to remove the retrospective application of the Illegal Migration Act which will allow decision-makers to decide asylum claims from individuals who have arrived in the UK since 7 March 2023 that have been put on hold.

On 21 August 2024, the Home Secretary announced new measures to boost Britain’s border security, including increased resource to target, dismantle and disrupt organised immigration crime networks.

On 4 October 2024, the Home Secretary agreed to the G7 Anti-Smuggling Action Plan, aimed at fostering closer cooperation with G7 partners to bolster border security, combat transnational organised crime, and protect vulnerable individuals from exploitation by migrant smugglers.

9. Related statistics

9.1 Small boat arrivals

• ‘Small boat activity in the English Channel’ – the Home Office publishes provisional daily and weekly numbers of small boat arrivals since 1 January 2018; however, figures in the Immigration system statistics quarterly release may differ from the provisional daily figures due to more time available for additional information to be recorded and additional quality assurance to be undertaken. Weekly data on small boats prevented from crossing the English Channel by French authorities can also be found on this link
• ‘Factsheet: Small boat crossings since July 2022’ - on 2 November 2022, the Home Office published a one-off factsheet on small boat crossings since July 2022, concentrating on Albanian arrivals in particular

9.2 Other migration statistics published by the Home Office

• ‘Statistics relating to Illegal Migration’ - an ad hoc statistical release that includes data relating to the asylum backlog, decisions, and caseworkers, small boat arrivals and enforcement activities
• ‘Immigration system statistics quarterly release’ - includes a range of data such as data on grants of protection and other leave, inadmissibility, immigration detention, returns, and visas
• ‘National Referral Mechanism statistics’ - data on referrals to the National Referral Mechanism, for potential victims of modern slavery