Inclusion Criteria:  Female patients aged ≥18 years ECOG performance status 0-2 Histologically proven diagnosis of high grade serous or high grade endometrioid carcinoma of the ovary, fallopian tube or peritoneum CT or MRI-confirmed disease relapse ≥ 6 months after day 1 of the last cycle of platinum-containing chemotherapy (cisplatin or carboplatin) and requiring treatment with further platinum-based chemotherapy Measurable disease by RECIST v1.1 or non-measurable disease supported by GCIG CA125 criteria of progression Most recent regimen must have included platinum (cisplatin or carboplatin) Must have responded to most recent platinum treatment by RECIST v1.1 or by GCIG CA125 response criteria Must have previously received a PARP inhibitor CA125 ≥ 100iU/l at screening Agree to provide additional research blood samples at the same time as blood draws prior to each carboplatin treatment, 6-weekly during surveillance and at 12- weekly follow-up visit Expected to be able to commence treatment within 28 days post randomisation Adequate bone marrow function Adequate liver function Adequate renal function Postmenopausal or women of child-bearing potential (WOCBP) must agree to have an urine or serum pregnancy test at screening for evidence of non-childbearing status and prior to trial treatment and use adequate contraception for duration of trial Willing and able to give consent and able to comply with treatment and follow up schedule  Exclusion Criteria:  Non-epithelial ovarian cancer, carcinosarcoma, low-grade serous and endometrioid carcinomas, mucinous & clear-cell carcinomas Patients requiring treatment with combination chemotherapy regimens Patients with a known hypersensitivity to carboplatin Persisting ≥ grade 2 CTCAE v5 adverse events/ toxicity (except alopecia and neuropathy) from previous anti-cancer treatment. Treatment with any other investigational agent, or participation in another interventional clinical trial within 28 days prior to randomisation. Major surgery within 14 days before anticipated start of treatment and patients must have recovered from any effects of major surgery. Evidence of any other disease, metabolic dysfunction, physical examination finding or laboratory finding giving reasonable suspicion of a disease or condition that contra-indicated the use of an investigation drug or puts the patients at high risk for treatment-related complications. Other psychological, psychiatric, social or medical condition, physical examination finding or a laboratory abnormality that the Investigator considers would make the patient a poor trial candidate or could interfere with protocol compliance or the interpretation of trial results. Malignancy treated within the last 5 years except: adequately treated non-melanoma skin cancer, curatively treated in situ cancer of the cervix, ductal carcinoma in situ (DCIS) of the breast, Stage 1, grade 1 endometrial carcinoma. Patients with symptomatic uncontrolled brain or meningeal metastases. A scan to confirm the absence of brain metastases is not required. The patient can receive a stable dose of corticosteroids before and during the study as long as these were started at least 4 weeks prior to treatment. Patients with spinal cord compression unless considered to have received definitive treatment for this and evidence of clinically stable disease for 28 days prior to randomisation. Pregnant or breast-feeding women are excluded. Women of childbearing potential will be excluded unless effective methods of contraception are used from signing of the informed consent, throughout the period of taking study treatment and for at least 6 months after last dose of trial drug(s). Inability to attend or comply with treatment or follow-up scheduling.