All participants will be asked to fast overnight (from 10 pm the night before), avoid strenuous exercise and smoking for 24 hours prior to attending a morning visit at the Exeter CRF/OCDEM (approx 2-4 hours depending on test choice). Participants will be asked to sign a written consent form prior to any data collection or test. Patients who lack capacity to consent will not be recruited. Participants will be given the opportunity to contact a member of the research team to discuss the project in more detail if desired. All participants will be informed of the nature and purpose of the study, its requirements and possible hazards, and their rights to withdraw at any time from the study without prejudice and without jeopardy to any future clinical care.