Recent work by the investigators group has identified that preserved endogenous insulin secretion is important for the glucose-lowering effect of a related class of glucose lowering therapies called GLP-1 receptor agonists, with little response seen in those with severe endogenous insulin deficiency. The investigators hypothesise that potentiation of endogenous insulin secretion may be the major mechanism of glucose lowering by DPPIV inhibitors and therefore those who have type 2 diabetes, but very low residual insulin secretion, will have little change in glucose with these medications. The pharmacodynamics of these agents (>90% inhibition of the target enzyme occurring within 45 minutes (for vildagliptin) and marked glucose lowering effect seen within an hour would allow us to explore this idea by assessing the impact of residual beta cell function on the glucose-lowering effect of a one-off dose of a DPP IV-inhibitor .