PART A Study visit 1 (30min, day 1): 1. Observations documented in CRF: resting heart rate and blood pressure 2. CGM sensor inserted. 3. Insulin dose reduced by approximately 15%. 4. Participants instructed to return on day 3 (study visit 2) fasted (no breakfast), and to refrain from exercising until then. 5. If they experience a hypoglycaemic episode within 24h of visit 2 then it will be postponed by 2 days. The medical research team will review the participant's insulin dose and make any required changes. If following this a second hypoglycaemia event occurs, then the participant will be withdrawn from the trial.

Study visit 2 (5 hours, day 3): 1. Observations documented in CRF: resting heart rate and blood pressure 2. Euglycaemic clamp for up to 1.5h to maintain blood glucose at 5mmol/L (90mg/dL) 3. Exercise challenge 4. If a participant fails to reach hypoglycaemia (defined as \<3.3mmol/L, 60mg/dL) during the exercise challenge, then the study visit will be repeated after at least 2 days of washout/rest. If they again fail to reach hypoglycaemia then they will be withdrawn from the trial. 5. If the exercise challenge is completed with a hypoglycaemia episode, then the participant will proceed to Part B.

Following visit 2, participants will be allocated to a treatment group using an adaptive randomisation scheme. This will be used to balance the groups' baseline characteristics (age, sex \& fitness level) in this relatively small pilot trial.

PART B Study visit 3 (30 minutes, day 8): 1. Observations documented in CRF: resting heart rate and blood pressure 2. CGM sensor inserted (if required). 3. Participants informed which arm of the study they have been randomised to, and supplied with their prescription of dapagliflozin. Participants in arm B1 will take the single dose when they attend study visit 4. Participants in arm B2 will begin taking their regular dose of dapagliflozin immediately. 4. Participants instructed to return on day 10 (study visit 4) fasted (no breakfast), and to refrain from exercising until then. 5. If they experience a hypoglycaemic episode within 24h of visit 4 then the exercise challenge will be postponed by 2 days. The medical research team will review the participant's insulin dose and make any required changes. If following this a second hypoglycaemia event occurs, then the participant will be withdrawn from the trial.

Study visit 4 (5 hours; day 10): 1. Observations documented in CRF: resting heart rate and blood pressure 2. (Arm B1): single dose of dapagliflozin taken when they arrive at the department unless they have experienced a hypoglycaemia event earlier in the morning. (Arm B2): compliance with dapagliflozin regimen and adverse events recorded in the CRF by the medical research team. 3. Euglycaemic clamp for up to 1.5h to maintain blood glucose at 5mmol/L (90mg/dL) 4. Exercise challenge 5. Participants in Arm B2 will be instructed to take one final dose of dapagliflozin the following day. All participants will be instructed to return to their pre-trial insulin dose after 48h 6. Arrangements made for end of study visit (either at CRU or home-visit).

Study visit 5 (30min; day 12-20): 1. End of study visit (either at CRU or home-visit) 2. CGM sensor removed and data downloaded. CGM system returned to CRU. 3. (Arm B1): adverse events recorded. (Arm B2): compliance with dapagliflozin regimen, adverse events recorded and any unused dapagliflozin returned (document drug accountability).

Telephone follow-up (15min; 19-27 days after study visit 5): 1. Documentation of any adverse events occurred following the discontinuation of dapagliflozin. 2. Participant informed about end of study