One to three days of sickness
You do not need a certificate.
Four to six days of sickness
Your employer may require you to complete a self certification form SC2 which is available from your employer or the DSS.
More than six days of sickness
You will need to see the doctor for him/her to issue a sickness certificate and for any subsequent renewal of that certificate. The only exceptions to this may be after hospital inpatient or outpatient attendance or for long-term sickness.
The law states that you do not need to obtain a certificate from your doctor for illnesses between 1-6 days. If your employer insists that you obtain one, this service is not covered by the NHS and a charge may be made.