Inclusion Criteria:

1. Patients over age of 18 years who are capable of providing written informed consent.
2. Confirmed diagnosis of ulcerative colitis by conventional clinical, endoscopic and histological criteria.
3. Failure of response to at least two weeks of oral prednisolone 40mg/day.
4. Active colitis as assessed by a Mayo score [21] of 6-12 inclusive (see Appendix 1)

Exclusion Criteria:

1. Patients under 18 or unable to give informed consent. 2. Patients in their first attack of ulcerative colitis. 3. Patients with severe ulcerative colitis as defined by presence of any of: temperature >37.5oC, pulse rate >100, focal severe or rebound abdominal tenderness, haemoglobin < 10.0g/dl, serum albumin <3.5 g/dl, transverse colon diameter greater than 5.0cms on plain abdominal X ray. 4. Patients who are pregnant, post partum (<3months) or breast feeding 5. Patients who are at risk of pregnancy and not using a reliable form of contraception (oral contraceptive and barrier or barrier plus spermicide). 6. Patients with a stoma 7. Positive stool culture for pathogens or test for C difficile at screening within 7 days prior to trial entry 8. Patients for whom a baseline Mayo score can not be reliably calculated: frequent use of laxatives (for proximal constipation) or antimotility agents (for control of diarrhoea) 9. Any change to maintenance medication for ulcerative colitis: azathioprine or 6-mercaptopurine within previous 3 months or 5-aminosalicylates within previous one month 10. Any change to rectal therapy for colitis within the previous two weeks. 11. Participation in other trials in the last 3 months. 12. Serious intercurrent infection or other clinically important active disease (including renal and hepatic disease)

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