You do not require a doctor's sickness certificate for any illness lasting less than seven days. Your employer may require you to complete a self-certification form (SC2) which is available from your employer or on the HMRC website.
Statement of Fitness For Work
If you are sick for more than seven days, your employer may ask for a Statement of Fitness for Work. Please telephone the Practice and we can arrange this for you, the Doctor may want you to make an appointment as part of the assessment.