Primary research question For adults surviving spontaneous (non-traumatic) symptomatic intracranial haemorrhage with persistent/paroxysmal atrial fibrillation/flutter (AF), does starting full treatment dose oral anticoagulation (OAC) result in a beneficial net reduction of all serious vascular events compared with not starting OAC? Trial design Investigator-led, multicentre, randomised, open, assessor-masked, parallel group, clinical trial of investigational medicinal product (CTIMP) prescribing strategies. We plan for a pilot phase, followed by a safety phase. Objectives Pilot phase: ~30 hospital sites keep screening logs and recruit at least 60 participants >24 hours after spontaneous symptomatic intracranial haemorrhage with AF and a CHA2DS2-VASc score ≥2 to determine the acceptability and feasibility of recruiting the target sample size in a definitive trial in an acceptable timescale. Safety phase: ~60 hospital sites will recruit at least 190 participants to determine whether the risk of recurrent symptomatic intracranial haemorrhage is sufficiently low (non-inferior) to justify a definitive trial. Eligibility criteria Inclusion: Spontaneous symptomatic intracranial haemorrhage, AF and a CHA2DS2-VASc score ≥2. Exclusion: Patient age