At the end of the run-in week, participants will then attend the outpatient clinic or day care ward research facility at the Oxford Children's Hospital or the Horton Hospital outpatient clinic in Banbury or the Royal Berkshire Hospital in Reading (Visit 2). At this visit, the subcutaneous glucose sensor will be inserted by the research nurse and children and young people and their families will be trained on its use prior to the study commencing. CGM records BG levels every 5 minutes over 7 days and thus provides much more information than routine BG testing. It also alarms to alert patients of high and low glucose levels. Children and young people will also record their BG levels from routine finger pricks, pre-prandially and before bed and on waking in the morning.