Screening visit (Visit 1, Week -3) Before any screening examinations take place potentially eligible research participants will be given a full explanation as to what participation in the study would involve - this will be done both verbally and in writing in the form of a written participant information leaflet. Potential research participants will be given sufficient time to consider their participation in the study and to ask any questions concerning the study. Potential research participants who are willing to take part in the study will be asked then to sign an informed consent form. No study related procedures will take place for any research participant before the informed consent form has been signed.