If you are off work due to sickness for 7 days or less, you do not require a GP certificate. It is your employer's responsibility to provide you with a self-certification form. This is also available from the HMRC Website
If you are off work due to sickness for more than 7 days, your employer may require a Fit Note to support statutory sick pay.
For more information, please see Fit Note Guide
Covid Fit Note/Isolation Note
If you are suffering with covid symptoms and are currently off work due to this or are currently having to self isolate due to covid please follow the link below to complete an isolation note for your employer.
Isolation note/Fit note