Brief Summary: This study aims to assess the effect, if any, on the adenoma detection rate of BowelScope bowel cancer screening flexible sigmoidoscopies by using the Endocuff Vision device.

Detailed Description: Colorectal cancer (CRC) is the fourth most common cancer in the UK with 40,000 new cases diagnosed annually. Most CRCs arise from the adenoma-carcinoma sequence which is a process that can take up to 10 years. Population screening programmes allow for earlier detection and removal of adenomas that may become malignant over time thus reducing CRC mortality. The English Bowel Scope Screening (BSS) programme began in 2013 and invites adults aged 55 and above for a one-off flexible sigmoidoscopy. The aim of the BSS programme is to reduce CRC development via the adenoma-carcinoma sequence through the detection and removal of adenomas from the left side of the colon. A large UK study has shown that offering one-off flexible sigmoidoscopy screening with adenoma clearance to adults aged 55-64 years reduced CRC incidence by 23% and mortality by 31%. Adenoma detection rate (ADR) is the most important marker of mucosal visualisation and is a surrogate marker of high quality colonoscopy. Data from colonoscopy studies have illustrated that a 1% increase in ADR is associated with a 3% decrease in interval colorectal cancer. In the BSS programme, ADR is comparatively lower the that shown in the initial sigmoidoscopy screening trials with a wide variation between endoscopists. Another marker that is often used is adenoma miss rates which also demonstrate a wide variation in clinical practice. Reasons for lesions not being detected at flexible sigmoidoscopy can be extrapolated from colonoscopy data and include; suboptimal technique; shorter withdrawal time; inadequate bowel preparation; presence of flat, depressed or subtle lesions; and the inability to visualise the proximal side of haustral folds, flexures (blind spots) and rectal valves. With the aid of the colonoscopic cuff Endocuff Vision®, the investigators aim to improve visualisation of the colonic mucosa by flattening colonic folds and manipulating them away from the field of forward view the investigators hypothesise that the Endocuff Vision® will improve adenoma detection rates by providing better fold retraction, a wider field of view and better scope tip stabilisation. This clinical randomised study will be conducted in subjects referred and scheduled for screening flexible sigmoidoscopy via the NHS English Bowel Scope Screening (BSS) Programme and will compare Endocuff Vision®-Assisted Flexible Sigmoidoscopy (EAFS) with Standard Flexible Sigmoidoscopy (SFS).