Inclusion Criteria:  The subject has given written consent to participate in the study. Diagnosed previously with UC (> 6 months earlier) determined by clinical and endoscopic histopathology (pathology showing chronic inflammatory changes). ≥1 documented previous flare-up and with last resolved flare >3 months away. Active UC determined by sigmoidoscopy before randomisation of study (baseline) and defined as a total Mayo index score of 4 to 10 points (endoscopic subscore ≥1, rectal bleeding ≥1). Permitted concomitant SoC medications include: Oral aminosalicylates (5-ASA), with a stable dose (1.6-4.8g/ day) for at least 12 days prior to screening, Visit 1. Steroids (dose ≤15mg at screening, Visit 1) with further tapering of dose in accordance with SoC until steroid tx termination. Immunomodulator, as: 6-Mercaptopurine, Azathioprine, Methotrexate (Stable dose for > 12 weeks prior to screening, Visit 1). Females of childbearing potential must use effective contraceptives  Exclusion Criteria:  Involvement in any investigational drug or device study within 30 days prior to this study Known intolerance of 5-ASA or sulphasalazine medications Biologics or FMT treatment less than 12 weeks before screening No 5-ASA or steroid topical treatment is allowed Antibiotic treatment < 1 month prior the study Unable to maintain stable dose of NSAIDs and PPIs Evidence of on-going extensive colitis Fever, defined as a temperature of >38.5 °C, at Visit 1 Anaemia, Hb value below 100 Evidence of on-going toxic megacolon Presence of obstructive diseases of the gastrointestinal system Any clinically significant concomitant disease that might interfere with patient safety Unwilling to withdraw probiotic supplements. Yoghurts without supplemented bacteria are permitted Pregnant Planned abdominal surgery Judged unable by the physician to comprehend information regarding the study