Fit Notes have replaced Sickness Certificates. You do not require a doctor's Fit Note for any illness lasting seven days or less. Your employer may however require you to complete a self-certification form (SC2) which is available from your employer or on the HMRC website. Download the form.
Evidence that you are sick
If you are sick for more than seven days, your employer can ask you to give them a medical certificate to support payment of SSP (statutory sick pay).
It is up to your employer to decide whether you are incapable of work. A medical certificate, now called a 'Statement of Fitness for Work’ (see below) from your Doctor is strong evidence that you are sick and would normally be accepted, unless there is evidence to prove otherwise.
For more information see The Fit Note: A guide for patients and employees.
You should be aware that the Department for Work and Pensions (DWP) is collecting anonymised data on the Fit Notes issued by your GP Surgery. The purpose of this is to inform government policy development. Further information can be found here.