In the event of an emergency call 999 and ask for the Police then Mountain Rescue. Provide them with the location of the emergency (grid reference, map number, mountain location and type of terrain. Number and names of people injured and their condition. You may need to provide... phone number of the phone you are using and any other phone numbers of people in your group. What actually happened. Time of the incident. Weather conditions at the site. What equipment you have with you. Any distinctive feature of the accident site.
While you are waiting for mountain rescue comfort the casualty (talking reassuringly to them), make sure that they are warm and if they are unconscious put them in the recovery position.
Once mountain rescue have been called you may need to direct them to your location. To do this give 6 blasts of your whistle or 6 torch flashes per minute: safety will soon arrive.