A British Bangladeshi (Bengali: ব্রিটিশ বাংলাদেশি) is a person of Bangladeshi origin who resides in the United Kingdom having emigrated to the UK and attained citizenship through naturalisation or whose parents did so; they are also known as British Bengalis. Large numbers of Bangladeshis emigrated to the UK, primarily from Sylhet, located in the north-east of the country, mainly during the 1970s. The largest concentration is in London, primarily in the east London boroughs, of which Tower Hamlets has the highest proportion, making up approximately 37% of the borough's total population. This large diaspora in London leads people in Bangladesh to refer to British Bangladeshis as "Londonis". Bangladeshis also have significant communities in Birmingham, Oldham, Luton and Bradford, with smaller clusters in Manchester, Newcastle upon Tyne, Rochdale, Cardiff, and Sunderland.

Bangladeshis form one of the UK's largest immigrant groups and are also one of its youngest and fastest growing communities. The population of Bangladeshis in Britain has grown steadily over the years. At the time of the 2001 UK Census, 154,362 Bangladeshi-born people were resident in the UK, and there were a total of 283,063 residents of Bangladeshi ethnicity. By 2007, the ethnic Bangladeshi population in England only was estimated to be 353,900. Estimates suggest there are about 500,000 Bangladeshis residing in the UK. Bangladeshis form a largely homogeneous community. Rates of unemployment are typically high, there is overcrowding, and some health problems. The latest generation of Bangladeshis, however, form a thriving community who are beginning to establish themselves in the mainstream of commerce and politics. Despite being the most recently settled of the major South Asian communities in Britain, the Bangladeshis are well established throughout the communities.