Many patients with scleroderma have damage to their kidneys caused by the disease. There is limited evidence for treatments to prevent this damage or stop it progressing. Blocking a substance in the blood called endothelin has helped treat some aspects of scleroderma. The purpose of this study is to see how effective a new endothelin blocker called Zibotentan is in treating patients who have scleroderma and have gone on to develop reduced kidney function as a complication. It will be given in addition to the accepted treatments used for scleroderma. There will be three parts to this study each for a different group of patients: