You only need a doctor’s note if you are unable to work and are ill for longer than seven calendar days. Your employer will provide you with an SC2 self-certificate form for shorter periods of illness. Sick notes can only issued from the date you see a doctor (GP or hospital doctor) and cannot be back dated.
Contrary to common belief hospital doctors can issue sick notes. If you require a sick note and are being seen in hospital insist on being issued a note there instead of having to book an appointment at the surgery. This will avoid inconvenience to you and save an appointment for another patient to be seen.