The investigators will recruit participants who have a clinical diagnosis of type 2 diabetes, are currently treated with insulin therapy and are known to have preserved or very low endogenous insulin secretion. Participants with and without severe endogenous insulin deficiency will be matched for clinical characteristics. Glucose variability, hypoglycaemic risk, and response to a single dose of a standard glucose lowering treatment will be assessed and compared between the groups. This will require 3 research visits over a 2 week period (one non-fasting, two fasting).