MARVEL: Mitochondrial Anti-oxidant Therapy to Resolve Inflammation in Ulcerative Colitis

Inclusion Criteria: • Active UC (Mayo of score 6 or greater with endoscopy subscore of 2 or more); or Partial Mayo Score 4-9 (e.g. without the endoscopic score) * Baseline rectal bleeding Mayo score of 1 or more * ≥18 years old * Confirmed diagnosis of UC confirmed on histology and endoscopic evidence for ≥3 months prior to screening. * Able to start taking prednisolone at the same time as the study drug/placebo * Subjects currently receiving the following treatment for UC are eligible providing they have been on stable dose for designated period of time * Oral 5-ASA or sulfasalazine stable dose for at least 4 weeks prior to inclusion and during the study period. * Azathioprine, 6-mercaptopurine stable dose for 8 weeks prior to study. * Topical treatment (5-ASA or steroid based) for active UC flare including suppository and enema. * Able and willing to give informed consent. Exclusion Criteria: * Severe extensive colitis as evidenced by: * Physician judgement that the subject is likely to require hospitalisation for medical care or surgical intervention of any kind for UC (e.g. colectomy) within 12 weeks of baseline. * Evidence of fulminant colitis, toxic megacolon or recent history of toxic megacolon within the last 6 months; or bowel perforation. * Evidence of acute severe UC fulfilling Truelove and Witts Criteria (\>6 bloody stools/day with evidence of any of these features: tachycardia \[\>90bpm\], fever \[\>37.8C\], anaemia \[Hb \<10.5g/dl\], low albumin \[\<30g/l\]). * Any current or previous biologic treatment including anti-TNF therapy or anti-α4β7 therapy; and oral JAK-inhibitors * Previous treatment for UC, except those listed in the inclusion criteria. * UC confined to proctitis (distal 15 cm or less) * UC with Primary Sclerosing Cholangitis (PSC) * Diagnosis of Crohn's disease or indeterminate colitis * Pregnancy (Current or attempting to become pregnant during trial period) or breastfeeding * Cyclosporine, mycophenolate, or tacrolimus administration within 8 weeks of screening. * Intravenous corticosteroids for treatment of colitis within 8 weeks of screening * Subjects with current - or recent history of - severe, progressive, or uncontrolled renal, hepatic, haematological, gastrointestinal, metabolic (including uncontrolled hypercholesterolemia), endocrine, pulmonary, cardiac, neurological disease. * Subjects who have positive stool examinations for enteric pathogens or Clostridium difficile toxin at screening. * Subjects with a known allergy/contraindication to MitoQ. * Subjects currently taking any products containing Mitoquinol mesylate (Coenzyme Q10) or any products containing Coenzyme derivatives such as Coenzyme A (CoA, SCoA, CoASH). If subjects are on these products, they can enter the trial after a 7-day washout period. * Subjects with current barriers in language or communication that in the judgement of local PI will impede the completion of the trial. * A history of overdose or suicide, or significant active mental health problems.