7 days off sick or less
If you're of work 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.
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.
How to count sick days
When you work out the number of days that you've been sick, you need to count all the days in a row you've been sick, including days you do not usually work, such as weekend or bank holidays.