You do not require a doctor's sickness certificate for any illness lasting seven days or less. Your employer may however require you to complete a self-certification form (SC2) which is available from your employer, at our reception or on the HMRC website
For any illness lasting longer than seven days you will usually need to see the doctor in order that they can issue a sickness certificate (Med 3) and for any subsequent continuation certificates.
"Signing-off" certificates are no longer issued, instead your final certificate should include the date on which you will be able to return to work.
If your employer insists on a certificate for an absence of less than 7 days or any additional evidence of your fitness for work this can only be provided as a private certificate for which a charge will be made.