Clinical Trial to Investigate Treatment With Photodynamic Therapy to Reduce Levels of Bacteria in Leg Ulcers

Inclusion Criteria: * Subjects will be males or females of non-childbearing status over 18 years of age. * Subjects will have a chronic leg ulcer with an ABPI ≥ 0.6 (measured at screening). * Subjects will have an ulcer that has been present for at least 3 months and not more than 3 years. * Subjects will have an ulcer with an area of 2 - 100cm2 and a maximum linear dimension of 10cm. * Subjects will have an ulcer with a total bacterial load of ≥ 104 CFU / cm2, determined within 2 weeks before the first treatment. * Subjects will have voluntarily signed and dated a subject Informed Consent Form (ICF). * Subjects will be, in the opinion of the Investigator, able to understand the study, co-operate with the study procedures and be willing to return to the clinic for all the required follow-up visits. * Subjects should be of appropriate health to participate in the study, as determined by the Investigator. This will be determined by a medical history, physical examination, 12-lead ECG and clinical laboratory evaluations. Exclusion Criteria: * Subjects under the age of 18 years of age. * Subjects who have taken topical or systemic antibiotics during the 2 weeks prior to screening. * Subjects who have used any anti-microbial dressing or topical antiseptic / antimicrobial or received maggot therapy during the 2 weeks prior to screening. * Subjects who have evidence of connective tissue disorders e.g. vasculitis or rheumatoid arthritis under active treatment. * Subjects who have any clinically significant medical condition that would impair wound healing as determined by the investigator, including uncontrolled diabetes as determined by HbA1C (\>12%) or immune disease. * Subjects who are known to abuse alcohol or drugs currently, or to have psychological disorders that could affect follow-up care or treatment outcomes. * Subjects who have received short course corticosteroids within 30 days prior to treatment. * Subjects who have participated in a clinical trial of any investigational drug within 4 months prior to treatment. * Subjects who have participated in a clinical trial of any investigational device, for example dressings, within 1 month prior to treatment. * Subjects who have previously been treated with IMP in this trial. * Subjects who have or are suspected of having malignancy, or who have received treatment for any active malignancy, apart from non-melanomatic skin cancer, within 3 months prior to treatment. * Subjects with evidence of exposed bone, tendon or facia visible around the target wound. * Subjects with photosensitivity disorders. * Subjects with systemic infection, whether or not related to their ulcer. * Subjects with clinically relevant (assessed by PI) active wound infection undergoing treatment.