You do not require a doctor's sickness certificate for any illness lasting seven days or less. Your employer may ask you to complete a self-certification form (SC2) which is available from your employer or on the HMRC website.
If you are under the care of a consultant, and need a sickness certificate because of a recent admission or operation, you should ask your consultant for your note. Consultants can give sick notes exactly like GPs can.
A professionals 'Fit note'
If you are unwell for more than seven days, your employer can ask you to give them medical evidence of your illness.
It is up to your employer to decide whether you are incapable of work. A medical certificate, (now called a 'Statement of Fitness for Work’) from your doctor is strong evidence that you are sick and would normally be accepted.
You could also provide evidence from someone who is not a medical practitioner, e.g. a dentist.
The 'fit note' was introduced on 6 April 2010. With your employer's support, the note will help you return to work sooner by providing more information about the effects of your illness or injury.
For more information see the DirectGov website (where this information was sourced)