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. In certain circumstances (e.g. where a patient has just been discharged from hospital after an operation) notes can be issued without the patient being seen by the doctor but this is not usually the case.