Every missed appointment costs the NHS money. If you are unable to attend an appointment it is vital you contact the surgery to cancel the appointment to make it available for another patient.
If you fail to attend an appointment, or the GP surgery is notified less than 30 minutes before the appointment time, this will be registered as a DNA or did not attend/failed to attend. Cancellations notified with less than 30 minutes warning will lead to an appointment slot not being used and a waste of GP resources.