Background Ethnic and socio‐economic inequalities have been reported in the uptake of colorectal cancer (CRC) screening. This study aimed to explore the factors affecting CRC screening participation in an ethnically and socio‐economically diverse inner city population. Methods Semi‐structured interviews were undertaken with 50 people aged 55–74 years, recruited from GP practices in south‐east London. Participants were from Black African (n=13), Black Caribbean (n=15), White British (n=17), Black other (n=2) and White other (n=3) backgrounds. Participants' socio‐economic status (SES) was assessed using a combined measure of educational attainment, housing tenure and car ownership. Participants' SES varied although there were more participants from less deprived backgrounds than those from more deprived backgrounds. The interview topic guide was informed by the Theoretical Domains Framework. Interviews were recorded, transcribed and analysed using framework analysis. Findings Lack of awareness of CRC screening was a barrier for all participants. There were also some notable group differences by ethnicity and SES. Cancer fear was a barrier for White British participants of varying SES. Misunderstanding instructions for completing the guaiac faecal occult blood test (gFOBt) was a barrier for people of low SES regardless of ethnicity. For Black African and Black Caribbean participants, of any SES, religious faith and a perceived civic duty to participate in screening encouraged participation. Discussion and conclusions This is the first study to provide detailed information on the separate views of Black African and Black Caribbean participants about screening. Consideration of ethnicity and SES together also allowed us to identify pertinent barriers for particular groups that can be targeted to improve access to screening for those who wish to take part.