Introduction Endoscopy services in the UK often supplement staffing through insourcing, yet the impact of this model on diagnostic outcomes remains unclear. This study evaluates differences in polyp and colorectal cancer detection between standard hospital endoscopists and insourced endoscopists at Sheffield Teaching Hospitals NHS Foundation Trust. Methods A retrospective observational study was conducted from March 1, 2022, to February 28, 2024, involving 2,173 diagnostic colonoscopies. All insourced procedures (n=1,205) were included, while a systematic one-in-five sampling approach yielded 968 hospital-based procedures. Only diagnostic colonoscopies were considered, excluding therapeutic, bowel cancer screening programme (BCSP), and inflammatory bowel disease (IBD) surveillance cases. All polyps identified during procedures were histologically matched through pathology records. Demographics and histological findings were compared between the two groups using chi-squared and t-tests. Results Patient demographics were similar across groups. Hospital endoscopists had significantly higher detection rates for tubular adenomas (21.2% vs. 14.9%, p<0.001), hyperplastic polyps (8.5% vs. 5%, p=0.001), and colorectal carcinoma (1.7% vs. 0.5%, p=0.003). Insourced endoscopists detected more villous/tubulovillous adenomas (3.2% vs. 1.3%, p=0.004). A higher percentage of procedures by insourced endoscopists yielded no polyp findings (73% vs. 63.5%, p<0.001). Conclusion Hospital endoscopists demonstrated higher detection rates for most clinically significant polyps and colorectal cancer. The findings suggest potential variability in diagnostic yield based on the endoscopist's role, warranting further evaluation of training, audit, and performance standards across staffing models.