Abstract. The article is devoted to the problem of the rapid growth of number of illegal migrants smuggled into the United Kingdom after the end of its exit from the European Union (Brexit, 31 December 2020) – during the transition period (1 February – 31 December 2020) and in the first part of 2021. The topic of illegal migration into the UK during its withdrawal from the EU (Brexit, 29 March 2017–31 December 2020) is considered in the article to the extent that it helps to highlight the different facets of the main subject of the research. Scrutinizing the genesis of the problem of illegal migration in the United Kingdom from 2003 to 2021, the article shows that the rapid rise of the migrants’ smugglings across the English Channel in small boats in 2020 – the first part of 2021 has become the challenge for the country. The termination of Great Britain’s membership in the European Union and the COVID 19 pandemic are regarded as the main reasons for it. The author enumerates actions made by the Boris Johnson’s cabinet which aimed at creating new legal framework for readmission of illegal migrants by the EU countries after the end of the transition period. The article pays attention to the strengthening of Anglo-French boarder cooperation as a way to cope with the transfer of illegal migrants to the UK. The creation of new British immigration law after the transition period is seen as a method of struggling with gangs of smugglers and as a means to curb rising influx of illegal migrants. The article considers the dependence of public and social security from tackling of illegal immigration as a source of the Islamist terrorism activity in the country. The author answers the question about the perspectives of the migrant transfer to Great Britain in the nearest future.