When do I need a fit note
7 days off sick or less
If you're off work sick for 7 days or less, your employer should not ask for medical evidence that you've been ill. Instead they can ask you to confirm that you've been ill. You can do this by filling in a form yourself when you return to work. This is called self-certification.
More than 7 days off sick
If you're off work sick for more than 7 days, your employer will usually ask for a fit note (or Statement of Fitness for Work) from a GP or hospital doctor. Fit notes are sometimes referred to as medical statements or a doctor's note.
Changes to who can issue fit notes
From 1 July 2022 nurses, occupational therapists, pharmacists, and physiotherapists will all be able to legally certify fit notes – something that at present only doctors can do. If you’ve been off work with illness for more than seven days, a fit note provides evidence to your employer about your absence and any relevant advice on how to support you to remain in or return to work.
Further information here