If you’re off work sick for seven days or less, your employer should not ask for medical evidence that you’ve been ill.
If you’re off work sick for more than seven days, your employer will usually ask you to provide evidence or proof that you’ve been ill. They will normally ask for a fit note from your GP. Fit note is the informal name for the Statement of Fitness for Work. Fit notes replaced sick notes from 6 April 2010.
The seven days include days that you don’t normally work. So when you work out how long you’ve been off sick, you should include weekends and bank holidays.
>Fit Notes (NHS Guide – external link)