If you are off work for five working days or less, no certificate is required. However, you may need to complete a self-certification form, which is obtainable from your employer.
If you are absent from work for five working days or more, because of illness, you may require a doctor’s certificate. In which case, you must arrange an appointment with a doctor; otherwise a certificate will not be issued
If for whatever reason, you require a doctor’s certificate covering a period of less than five working days, a private certificate can be issued at an appointment; there will be a charge for such a certificate.