All employees should be able to "self-certify" themselves as too sick to work for the first seven days of illness. Forms for self-certification can be obtained from your employer or downloaded from the Department for Work and Pensions (DWP) website (http://dwp.gov.uk)
Following this period a doctor's note is required. Such requests for sick notes should preferably be made during morning surgery. In certain circumstances (eg where a patient has been discharged from hospital after an operation) notes can be issued without the patient being seen by the doctor.