This research project is designed to find out whether people who suffer repeated urinary tract infections (UTI) related to the need to empty their bladders intermittently with a fine plastic tube (catheter); a process called clean intermittent self-catheterisation (CISC), benefit from taking continuous daily low-dose antibiotics (antibiotic prophylaxis). The investigators estimate that about 40,000 people in the United Kingdom need to use CISC regularly to empty their bladder either because of nerve damage such as multiple sclerosis or because of failure of the bladder muscle to contract, and of these about 25% (10,000 people) suffer frequent UTI. One way to reduce this problem may be to take a small daily dose of antibiotics and the study aims to find out whether such treatment is effective and worthwhile both for the people who suffer the problem and for the National Health Service (NHS).