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.
You should get a fit note from the doctor who is treating you. This will usually be your GP, but if you are getting treatment in hospital you should ask for one from your hospital doctor (if you don’t already have one) Your GP will not issue a Fit note. The only exception to this rule will be if you have been admited to A&E. Fit notes can either be handwritten or printed, but must be signed by a doctor. Duplicate fit notes can only be issued if the original has been lost.
The fit note is classed as advice from your doctor. Your employer can decide whether or not to accept it, and your doctor cannot get involved in any disputes between you and your employer.