BACKGROUND: Sexually active young people attending London further education (FE) colleges have high rates of chlamydia, but screening rates are low. We will conduct a cluster randomised feasibility trial of frequent, rapid, on-site chlamydia testing and same-day treatment (Test and Treat (TnT)) in six FE colleges (with parallel qualitative and economic assessments) to assess the feasibility of conducting a future trial to investigate if TnT reduces chlamydia rates. METHODS: We will recruit 80 sexually active students aged 16-24 years from public areas at each of six colleges. All participants (total n = 480) will be asked to provide samples (urine for males, self-taken vaginal swabs for females) and complete questionnaires on sexual lifestyle and healthcare use at baseline and after 7 months. Participants will be informed that baseline samples will not be tested for 7 months and be advised to get screened separately. Colleges will be randomly allocated to the intervention (TnT) or the control group (no TnT). One and 4 months after recruitment, participants at each intervention college (n = 3) will be texted and invited for on-site chlamydia tests using the 90-min Cepheid GeneXpert system. Students with positive results will be asked to see a visiting nurse health adviser for same-day treatment and partner notification, (backed by genitourinary medicine follow-up). Participants in control colleges (n = 3) will receive 'thank you' texts 1 and 4 months after recruitment. Seven months after recruitment, participants from both groups will be invited to complete questionnaires and provide samples for TnT. All samples will be tested, and same-day treatment offered to students with positive results. Acceptability of TnT will be assessed by qualitative interviews of purposively sampled students (n = 30) and college staff (n = 12). We will collect data on costs of TnT and usual healthcare. DISCUSSION: Findings will provide key values to inform feasibility, sample size and timescales of a future definitive trial of TnT in FE colleges, including: Recruitment rates TnT uptake rates Follow-up rates Prevalence of chlamydia in participants at baseline and 7 months Acceptability of TnT to students and college staff Estimate of the cost per person screened/treated in TnT versus usual care TRIAL REGISTRATION: International Standard Randomised Controlled Trials Registry, ID: ISRCTN58038795 , Registered on 31 August 2016.