Participants and recruitment: The investigators will recruit 54 participants. Potential participants will be identified from existing research cohorts or routine clinical practice where endogenous insulin status (C-peptide in blood or urine) has been previously assessed. Where patients are identified from existing cohorts who have given consent for future contact, a letter from that database administrator will be sent providing generic information on the study. Contact details of those interested in further information will be passed to the research team to continue the recruitment process. Where potential participants are identified in clinical practice they will be given generic information about the study by their clinician and if interested, and with their permission, their contact details will be passed to a member of the research team for further contact. The research team will be responsible for the recruitment process.