You do not require a doctor's sickness certificate for any illness lasting 7 days or less. Your employer, however, may require you to complete a self-certification form (SC2) which is available from your employer or at our front desk or can be downloaded here: Self Certification Form.
For any illness lasting longer than 7 days you will need to speak to the doctor for a sickness certificate (Med3) to be issued and for any subsequent renewal of the certificate. A sickness certificate cannot be pre-dated (i.e. issued before the date on which it starts) but certificates can overlap if required. If your employer insists on a sickness certificate for 7 days or less a fee will be charged.