In the land of Flying Doctors, we've a well established priority system of MED1 and MED2 medical emergency designators. Not at all sure if there is any ICAO equivalent obviously nothing similar in the UK. Without getting the definitions, MED1 are life-critical flights, and are afforded the highest priority in Australia under aircraft in distress (MAYDAY/PAN). The seas won't generally part but they mostly get no delay. MED2 are ambulance flights of lesser urgency and are afforded the same priority as RPT.