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 or on the HMRC website.
Evidence that you are sick
If you are sick for more than seven days, your employer can ask you to give them some form of medical evidence to support payment of SSP (statutory sick pay).
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’ (see below) from your doctor is strong evidence that you are sick and would normally be accepted, unless there is evidence to prove otherwise.
You could also provide evidence from someone who is not a medical practitioner, e.g. a dentist. Your employer will decide whether or not this evidence is acceptable. If your employer has any doubts, they may still ask for a medical certificate from your GP.
Statement of Fitness for Work - ’Fit Note'
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)
It is not the policy of general practice to provide medical certification for school absence and the practice policy is to decline such requests. There is an agreement between the Department of Health and the Department of Education that they are not necessary or appropriate. In line with the procedure for adults to self-certify, it is suggested that schools adopt a similar policy, whereby the child's parent, or legal guardian, or carer, provides a note explaining why the child is off school. Alternatively, schools could utilise the school nursing service to provide these notes if they deem the note from the parent/guardian/carer is not sufficient. GPs have no legal or contractual obligation to provide sick or fit notes for children and if under any specific circumstances they decide to do so, this is deemed as private (non-NHS) work and will attract a fee for undertaking this work.