 This open label, randomised, controlled, multi-centre study will assess the efficacy and safety of single agent olaparib vs. standard of care, based on physicians choice of single agent chemotherapy i.e paclitaxel, or topotecan, or pegylated liposomal doxorubicin, or gemcitabine in platinum sensitive or partially platinum sensitive relapsed ovarian cancer patients who carry germline deleterious or suspected deleterious BRCA mutation and who have received at least 2 prior lines of platinum based chemotherapy. Patients are eligible to undergo BRCA testing even if they have not yet had recurrence or progression of disease 6 months 183 days after completion of their last platinum therapy. 