Abstract Background Uptake of colorectal cancer screening is low in the English NHS Bowel Cancer Screening Programme (BCSP). Participation in screening is strongly associated with socioeconomic status. The aim of this study was to determine whether a supplementary leaflet providing the ‘gist’ of guaiac-based Faecal Occult Blood test (gFOBt) screening for colorectal cancer could reduce the socioeconomic status (SES) gradient in uptake in the English NHS BCSP. Methods The trial was integrated within routine BCSP operations in November 2012. Using a cluster randomised controlled design all adults aged 59–74 years who were being routinely invited to complete the gFOBt were randomised based on day of invitation. The Index of Multiple Deprivation was used to create SES quintiles. The control group received the standard information booklet (‘SI’). The intervention group received the SI booklet and the Gist leaflet (‘SI + Gist’) which had been designed to help people with lower literacy engage with the invitation. Blinding of hubs was not possible and invited subjects were not made aware of a comparator condition. The primary outcome was the gradient in uptake across IMD quintiles. Results In November 2012, 163,525 individuals were allocated to either the ‘SI’ intervention (n = 79,104) or the ‘SI + Gist’ group (n = 84,421). Overall uptake was similar between the intervention and control groups (SI: 57.3% and SI + Gist: 57.6%; OR = 1.02, 95% CI: 0.92–1.13, p = 0.77). Uptake was 42.0% (SI) vs. 43.0% (SI + Gist) in the most deprived quintile and 65.6% vs. 65.8% in the least deprived quintile (interaction p = 0.48). The SES gradient in uptake was similar between the study groups within age, gender, hub and screening round sub-groups. Conclusions Providing supplementary simplified information in addition to the standard information booklet did not reduce the SES gradient in uptake in the NHS BCSP. The effectiveness of the Gist leaflet when used alone should be explored in future research. Trial registration ISRCTN74121020 , registered: 17/20/2012.