For sickness less than seven days
If you have been sick for less than seven calendar days, you do not need a doctor’s note.
Your employer will provide you with an SC2 self-certificate form or you can complete this online SC2 form on gov.uk: Statutory Sick Pay form.
For sickness more than seven days
A doctor can provide you with a fit note (sick certificate) if they have seen or spoken to you about the medical problem. Request or renew your renew your sick certificate by submitting ‘admin query’ on Engage Consult or calling the surgery.
If you have not seen a doctor, book an appointment and they can issue you a sick certificate after the appointment.
NHS Guidance
The NHS provide useful guidance: Getting a fit note – NHS