I'm not sure what the abbreviations are in the UK, but here in the states they are as follows;

GN - Graduate Nurse (after graduation but before you take the boards)
LPN - Licensed Practical Nurse
LVN - Licensed Vocational Nurse (like an LPN)
RN - Registered Nurse (higher level of training than LPN/LVN)
ADN - Associates Degree in Nursing (an RN with a 2 year degree)
BSN - Bachelors of Science in Nursing (an RN with a 4 year degree)
ARNP - Advanced Registered Nurse Practitioner (Masters level RN)
CRNA - Certified Registered Nurse Anesthetist (Masters level also)
PA - Physician's Assistant (ARNP wannabes )
CCRN - Critical Care Registered Nurse
CNA - Certified Nursing Assistant
CMA - Certified Medical Assistant
EMT - Emergency Medical Technician
EMT-P - Paramedic
OT - Occupational Therapist
RT - Respiratory Technician (Therapist?)

I can't think of any more off the top of my head. Maybe someone can add to this?