I think NHSdirect actually produces something like that - it's card sized but folds out to an A4 sheet, and has basic guidelines for when you should call an ambulance, when you should call an emergency doctor, when you should call the NHS direct number, when you should make an appointment with your GP, when you should just ask your pharmacist for advice and so on. I think it also has a list of what should be in a basic home medicine cabinet.