INTRODUCTION: The incidence of anal carcinoma is increasing, with the current gold standard treatment being chemoradiotherapy. There is currently a wide range in the radiotherapy dose used internationally which may lead to overtreatment of early-stage disease and potential undertreatment of locally advanced disease.PLATO is an integrated umbrella trial protocol which consists of three trials focused on assessing risk-adapted use of adjuvant low-dose chemoradiotherapy in anal margin tumours (ACT3), reduced-dose chemoradiotherapy in early anal carcinoma (ACT4) and dose-escalated chemoradiotherapy in locally advanced anal carcinoma (ACT5), given with standard concurrent chemotherapy. METHODS AND ANALYSIS: The primary endpoints of PLATO are locoregional failure (LRF)-free rate for ACT3 and ACT4 and LRF-free survival for ACT5. Secondary objectives include acute and late toxicities, colostomy-free survival and patient-reported outcome measures. ACT3 will recruit 90 participants: participants with removed anal tumours with margins ≤1 mm will receive lower dose chemoradiotherapy, while participants with anal tumours with margins >1 mm will be observed. ACT4 will recruit 162 participants, randomised on a 1:2 basis to receive either standard-dose intensity modulated radiotherapy (IMRT) in combination with chemotherapy or reduced-dose IMRT in combination with chemotherapy. ACT5 will recruit 459 participants, randomised on a 1:1:1 basis to receive either standard-dose IMRT in combination with chemotherapy, or one of two increased-dose experimental arms of IMRT with synchronous integrated boost in combination with chemotherapy. ETHICS AND DISSEMINATION: This study has been approved by Yorkshire & The Humber - Bradford Leeds Research Ethics Committee (ref: 16/YH/0157, IRAS: 204585), July 2016. Results will be disseminated via national and international conferences, peer-reviewed journal articles and social media. A plain English report will be shared with the study participants, patients' organisations and media. TRIAL REGISTRATION NUMBER: ISRCTN88455282.