Venesection will take place at 10 days, 3, 6 and 12 months post-operatively and yearly thereafter for fasting glucose and HbA1c as part of the routine care of patients of the obesity clinic. As part of clinical management we will ensure that all patients with diabetes will have a kidney (2 samples of morning urine albumin creatinine ratio), nerve (nerve conduction study, including thermal threshold testing) and eye (retinal photograph) tests once before and within 1, 2 and 3 years after surgery. These tests are all non invasive and except from the nerve tests are performed routinely for all patients with diabetes at least yearly and if performed in the community they will not be repeated.Therefore, other than the nerve conduction studies, there will be no extra burden to the patients as a result of the study.